Meet Hardy.

Our founder has been living and breathing swimming pools for over 25 years. Starting from a backyard garage in Central Coast’s Gosford with a single van sorting out people's pools, there's nothing Hardy doesn't know about pools. If he doesn't know about it, then it's not worth knowing!

For the first time ever, we're giving you an exclusive look at his personal notebook which contains a quarter of a century's pool knowledge, distilled into its purest form. No extras here, just pure, unadulterated knowledge on keeping your pool crystal-clear, straight from the mind of Mr Pool Man Himself.

Water Chemistry

Understanding your pool Means understanding Water Chemistry. There are

  • pH
  • Total Alkalinity
  • Calcium Hardness
  • Stabiliser (Sunscreen, UV Blockout)
  • Water Balance
  • TDS or Total Dissolved Solids
  • Chlorination Testing
  • Algae Control


Personal Notes

The pH level I think is the most important factor in the water chemistry of a swimming pool.

Feel even more important than the CHLORINE, because unless the pH level stays within certain limits, there is little point chlorinating the pool.

The technical definition of pH is a reading of
“The logarithm of the reciprocal of the hydrogen ion concentration”, of the water being tested or more simply the “percentage of hydrogen ions”.

Water in any form is either acidic, neutral, or alkaline.

Water with a pH of 7.0 is neutral and from 7.0 to 0.0 is acidic(the lower the pH figure, the stronger the acidic condition. From 7.0 up to 14.0, the water becomes more alkaline with 14 being the highest.

When the water is acidic below 7.0 “HYDROGEN IONS” are produced and the lower the reading, the more hydrogen ions are produced.


Chemical Formula

CHLORINE, when added to the water forms hydrochloric acid and hypochlorous acid.

(Chemical formula)

CL2       + H2O   = HCL       +     HOCL

Chlorine   Water   hydrochloric     hypochlorous

Then the Hypochlorous acid is the MAIN component in the KILLING of BACTERIA, ALGAE, GERMS, removing colour, odour, and taste, and oxidizing out organic material is broken down again.

This is the whole basis of CHLORINE WATER TREATMENT, as the amount of hypochlorous acid and or the amount of hydrogen and hypochlorite ions formed depends upon the pH of the water.

NOTE: this is a reversible reaction.

Thus, by changing the pH, the most desired, most economical usage of hypochlorous acid, or simply, chlorine can be obtained.


The main reason to watch the pH level in your pool water

pH % Hypochlorous acid % Hypochlorite Ion
















If a pool has a pH of 8.0 ( which many people allow their pool water to rise to), then it is needed to use 2-3 times the amount of chlorine to obtain the same amount of hypochlorous acid or usable FREE Available Chlorine (F.A.C) in the water.

This is very UNECONOMICAL.

Our body and eyes have a general pH of 7.3-7.5 and anything below that will cause skin and eye irritation, remember pH 7.0 to 8.0 is a TEN times increase in hydroxyl ion concentration.

The higher the pH rises, the more chance the water will become unbalanced and allow depositing of chemicals on the finished pool surface whether you have sand, DE, or Cartridge filter.

Factors Affecting pH

  1. The impurities which come in with the chlorine dosage.
  2. Adding water to the pool or rainwater.
  3. Dust being blown in from the yard (i.e. fire)
  4. Organic matter carried in by swimmers.
  5. Organic compounds secreted into the water from human bodies whilst in the water.

Because the pH controls the amount of F.A.C (free available chlorine) it is the most important and the first factor to consider in your pool treatment.

Controlling pH

pH must be controlled to our best possible usage. This can be done by either adding acid or alkali of a known concentration, depending upon the amount of water in the pool and the pH change required.

As with any other chemical level in your pool, a good testing kit is required to accurately give you the current reading so that adjustment calculations can be done accurately.

Basically, this answers the question: "How do we know what the pH is, how much we want it changed and how much of what is needed to affect that change?"

Other facts to remember about pH

  1. Testing of pH can be done at any time of the day, at least once a week.
  2. When doing a pH test, always do so with a chlorine remover in the sample
  3. Always take the sample from at least 20cm below the water level, because many substances which can give high pH readings, tend to float on top of the water.
  4. Try to use the same background colour when testing and taking readings, otherwise incorrect readings will result from ie: a clear or cloudy day.
  5. When the pH falls below 7.3 the formation of chloramines increases giving rise to sore eyes, smell and taste of chlorine, and bad sanitization of the pool.

The majority of swimming pool water problems occur because of incorrect pH control. By the time a person has cloudy water in the pool that water has had an incorrect pH level for two to four weeks so some damage has been done with scaling or clogging of the filter.

Too low pH has extreme effects on any metals which may be in the water or the filtration system. The metals are drawn into the water by corrosion then become a metallic ion then when chlorine is added the ions oxidize to form colored clouds in the water either green or red for iron oxides, or black or blue for copper oxides, or black for radioactive oxides.

Total Alkalinity

Total Alkalinity, as a figure for use in swimming pools, DEPENDS on 2-3 other major factors.

  • pH
  • Calcium Hardness
  • Water temperature

Total Alkalinity in normal make-up water may vary considerably from place to place throughout different places in Australia, so always suggest testing the alkalinity level of the local water supply.

ie. The levels can change from place’s like Darwin in the NT where the total Alka is usually 10-20ppm to a place 500km away like Kathrine which has a total Alka of 400ppm to other places in QLD which can have to 1000ppm

All of these levels can be worked with if the knowledge and testing equipment are available. The levels may have changed slightly such as in Darwin where the level would have to be increased to approx 80-120ppm to buffer the pH. In other parts of QLD, the total Alka would have to be lowered to 70-80ppm to soften the water a little. In general, keeping with current methods in Australia total Alka must be kept within the range of 80-120ppm.

At lower levels of Alkalinity, the pH of the water tends to bounce

This means we do a pH test and it shows 6.9 followed by a base demand test which shows how much buffer we need (e.g. 1.0kg Buffer) The buffer is added and tested again 4-5 hours later showing a pH of 7.9 instead of 7.4. Leaving it for another 2-3 hours the test shows a 7.0 reading, even though we used the correct amount of Buffer.

This reaction is brought about by the fact that when Buffer is added, reactions occur where large numbers of hydroxyl ions are formed thus raising the pH.

However, because the total Alka products are also made up of hydroxyl ions then the want for these ions will remove them from a situation where they can keep the pH up. This then allows the pH to bounce back down.

There is no real high limit unless the Total Alkalinity presents a problem with water balance.


Calcium levels in your pool matter

In some cases, a very high Calcium level will also help buffer the pH but it also tends to force it up gradually.

There is a pool that runs 900ppm calcium hardness and 20ppm in total Alkalinity but does not have a pH bounce.

The problem does occur more where the Alkalinity is naturally low and needs to be kept up. In the pool just mentioned, the Alka must be held down continually, so acid added for pH control is greatly absorbed by the Alkalinity in keeping that down - thus giving a very slow reaction with the pH.

Before we go into the methods of Total Alkalinity, we must first bring to mind the meaning of the term “milligrams per liter”. This means one milligram in one liter or one gram in 1000 liters or 60 grams in 60000 liters of water. 60000 liters is an average size pool.

Therefore, if there is an Alkalinity of 90ppm, there is 4.0 kg of buffer solids in 45000 liters of water.

Alkalinity Control

Testing - To test for Alkalinity in the pool water, a titration test is done. In this test, take a known volume of the pool water and add to it an indicator that changes color dependent upon the acidity or alkalinity content of the water.

Usually, Bromecresol green or Blue are used, thus giving a green or blue colour to the sample. In Australia, it is mainly blue.

Next, a very dilute but known strength of Sulphuric acid or reagent is added drop by drop and counted to the point where the alkali salts have absorbed enough acid to neutralize themselves; the indicator then changes color.

The number of drops is then multiplied by 10 and the answer is the Total Alkalinity in ppm.

Alkalinity Testing Results

If the Alkalinitty reading is high - an adjustment is needed downwards, then this can be read directly off an Alkalinity Chart and will answer liters of Hydrochloric acid depending upon the size of the pool.

But remember the Hydrochloric acid will also lower the pH: if this is not required, then compensation must be made, by using Soda Ash at a later stage to increase the pH.

If the Alkalinity reading is low - an upwards adjustment is required, then this can be directly read off an Alkalinity chart. By the addition of Sodium Bicarbonate, we can raise the Alka to the desired level.


No Hard Rules!

There are no real bounds to Alkalinity

In very soft water areas where the Alka is around 20-30ppm and the calcium hardness is 30-40ppm raising the Alka to 600-700ppm may not be detrimental.

Remember, the main reason for control of Alkalinity is:

1.To control pH movement.

2.To help with water balance.

NOTE: Sodium Bicarbonate can only ever raise to a maximum of 8.3 which is its own pH.

Personal Notes:

It is generally taught in Australia never to add more than 1.0 liter of acid at any one time.

This is a handy but unscientific approach to the system. By testing the water correctly for all components of water balance, then calculating how much acid could be added before total alkalinity would no longer absorb the acid and change the pH. Then the correct amount could be added at once.

As an example, there is a town in Australia where up to 10 liters of Hydrochloric can be added to a 60000-liter pool in one go without any pH change. This was only found by correct and proper testing and analyzing before treatment was begun.

Don’t take the meaning and action of Total Alkalinity lightly, as understanding it, utilizing, and controlling it can make work a lot easier.

- Hardy

Calcium Hardness

Calcium Hardness, often neglected

Calcium Hardness is neglected by a very high percentage of swimming pool service and advisory staff for two reasons.

  • They were not aware it was necessary.
  • They don’t know how to use the figures if they had them.

Calcium Hardness is a measure of all the calcium found in different calcium compounds in the pool water. Eg: Calcium carbonate, calcium Hydroxide, calcium bicarbonate, etc.

It is a relatively stable factor in water hardness but can be utilized as it is or changed using different methods.

Calcium Hardness, low test results

A known size sample of pool water is taken and a calcium buffer is added to it. This gives a standard for the neutralizer to work from. An indicator is then added to the liquid to form a color and then drops of the neutralizer are added.

When the colour changes, the number of drops are counted and multiplied by 10. The answer is calcium hardness in mg/1.

If Calcium Hardness is too low in a pool, it does not usually cause too many problems as long as the alkalinity is adjusted accordingly. If it is too low, it can be increased by the use of Calcium Chloride as per a given chart. This is very useful in soft water areas.


Calcium Hardness, high test results

If too high, the Calcium Hardness can be lowered by the use of a precipitation situation. To do this, the pH must be increased to 8.3 - calculate this by use of the base demand test, then adjust the alkalinity to give the water balance at pH 8.0 What will happen, works on the following principle:

The water of a fixed volume at a given temperature and a fixed pH can only hold a certain amount of solids in the form of carbonates and bicarbonates, thus if we raise the pH to 8.3 by adding sodium bicarbonate, the alkalinity will rise the point where the water cannot hold any more solids

It is at this point that allows the calcium salts to come out of solution as a (white cloud/cloudy water) and with the use of a light flocculant they can be precipitated to the floor and ideally vacuumed to waste.

Very Important note about Calcium

Calcium that naturally precipitates when the pH or Total Alkalinity is allowed to rise too high is one of the primary causes of cloudy waters, stained interior finishes, clogged filters, and somewhere for algae and bacteria to grow, so control it.

Stabiliser (Cyanuric Acid, Sunscreen, UV Blockout)

Stabiliser (Cyanuric Acid, Sunscreen, UV Blockout)

This also is another factor commonly overlooked, if the stabiliser level is too high in the pool, no amount of Chlorine you add to your pool will change the GREEN pool.

Saltwater pools: Recommended levels are 60-80ppm

Non-Saltwater Pools: Recommended levels are 30-50ppm

And if the pool is in a lot of direct sunlight keep it in the higher end.

Its purpose is to stabilise the chlorine in your pool water, so sanitizer lasts longer. And this where you have a certain amount of FREE chlorine to sanitise your pool

Total Chlorine is the combined chlorine with what is wrapped up with a stabiliser in the pool.

The biggest mistake a lot of people make today is totally relying pool chemicals with a built-in stabiliser, and realizing as the pool needs more chlorine, more and more stabilized chlorine gets added, thus this also continually increases the stabilizer level so high, the only way forward is to drain half the pool and start again.

Update: Enzymatic products are now available on the to safely reduce cyanuric acid levels.

While there is now a solution to get rid of cyanuric acid in pools, it's still best (and more budget-friendly) to be mindful of cyanuric acid levels in your pool whenever adding pool chemicals that contain built-in stabiliser.

Water Balance

Water Balance, what is it?

In a nutshell, water can and will always try to balance its levels physically, it also tries to balance itself CHEMICALLY.

LSI or Langelier Saturation Index

As mentioned above on Calcium Hardness, water has a point where it holds a certain amount of Bicarbonates and Calcium at one time dependent upon temperature, pH, and a constant volume of water. And considering all the above points and applied to a certain set of tables known as a “LANGELIER INDEX” or "LSI" and from this, you will see if the water is IN or OUT of balance.

There are no one set figures which gives us a water balance but many thousands of sets. Eg: at pH 7.4 one can obtain approximately 1000 variations of figures of Total Alka and Calcium Hard which will give you balanced water.

Even though there are so many combinations for balanced water, in most cases, it is out of balance.

Click here for a more detailed look at LSI.

No Simple Solution

No matter what anyone says, it’s not sufficient to know just the pH and correct it to 7.4 and test Alkalinity and adjust that to 80-120ppm. The Water balance could still be way out and still cause problems. It also depends on Calcium Hardness and your Stabilizer level as well - so taken that your volume is constant and temperature in the range of 20-40 degrees Celsius, then the four factors must be known are:

  • pH
  • Total Alkalinity
  • Calcium Hardness
  • Stabilizer

Why is Water Balance so Important?

Too much POSITIVE imbalance can or will cause:

    • Precipitation(Scaling) of Calcium or bicarbonate onto the pool walls and floors, coating the internal walls and pipework, it can also deposit large amounts of calcium or bicarbonates in the filter media whether it be sand or cartridge. This will lessen the life of the media or cartridge and becomes costly to the pool owner for either.
    • If deposits form on the walls and floor of the pool it also provides a place for algae to grow and feed on.
    • It also attracts water beetles while it is suspended in the water.
    • When the walls become coated, they will usually change colours depending upon the salts which are coming out of the solution - a stain will form on the walls or floor, it may off white, light brown, or light grey but regardless it is unsightly and shows a lack of maintenance on the part of the owner and this usually reflects back to the lack of teaching on the part of the pool handover man or pool Shop.
    • If there is a heater in the system the water passing through usually heats above 40 degrees causing more imbalance in which case the water tends to release larger amounts of salts to try and regain balance.
    • When this happens the salts form a coating on the inside of the piping and all the internal metal heaters which can damage but also reduces the transfer qualities and the efficiency of the heater.
    • A high positive imbalance can give the feeling of hard water and be uncomfortable to swim in.

Too much of a NEGATIVE imbalance in water can and will cause:

    • Etching of metal pipework pumps filters, and even chrome-plated ladders and fittings if strong enough.
    • Etching of the cement in the walls of the marble sheen finished pools.
    • The disintegration of the same base materials in vinyl liners eventually leads to them coming apart from the liner.
    • Acid affects eyes and skin which is irritating.
    • And a decomposing of filter mediums whether they be sand or cartridge.


As you can see, water balance is extremely important!

Sample Adjustment - 45,000L Pool

Sample Reading:

  • pH 7.2
  • Total Alkalinity 42
  • Calcium Hardness 225
  • BDR 1 drop


Using a Langelier Index Chart, run a straight line across the Total Alkalinity and Calcium Hardness and it shows to have balanced water, a pH of 8.0 is needed. This is too high for the Effective use of Chlorine, so -

Remember that calcium level is the most stable and hardest to move so call it our set point.

With a straight-line graph on the set point of 225ppm Calcium Hardness on the Langelier Index scale, run a straight line through the pH at 7.4 ( our Optimum pH ) and read of the required Total Alkalinity, which will be a figure of 130ppm.

At these figures of 225ppm Calcium Hardness, 7.4 pH, and 130ppm Total Alkalinity, the water is perfectly balanced which is neither etching nor scaling.

Correct Way to Balance Your Pool Water

First Steps

Firstly, we consider our Base Demand Test                  

(From BDR chart) of 160 gms of Soda Ash to raise the pH to 7.4 (Note this is Soda Ash).

Secondly, take the Total Alkalinity up and has to be raised from 42 - 130ppm (a 90 mg/l rise) so 90 mg/l in 45 000 liters will need approx 7.0 kg of Bicarbonate(Buffer)

(Note this - 7.0 kg Bicarb)

Remember, when Bicarb is added, it also increases the pH of the water by approximately 0.1 points on the pH scale for each 10 mg/l increase. Therefore, the pH could easily rise to 8.1 when the Bicarb is added so there is NO need to add the Soda Ash.

The Balancing Act

Now see why the whole treatment must be worked out carefully before beginning. If the Soda Ash had been added a pH of 8.4-8.6 would have occurred.

The Total Alkalinity is correct now but the pH is too high, so - for every 2 points above 7.4, we add .7 Liters of Acid. In this case, the ph is 8.0-8.1 needs 1.7 Litres of acid to correct the pH.

However, another problem arises. The addition of acid also lowers the Total Alkalinity. Checking with the chart, it shows 1.7 liters of acid to a 45000-liter pool lowers the Alkalinity by 22ppm, so, therefore, to raise it initially NOT 90ppm, but 112ppm. So increase the Bicarb to 9.0 kg, not 7.5kg.

The above is the scientifically analyzed pool which can be performed with a Photometer, and when the above is applied to the pool water, Water is balanced.

Visual Representation of Balancing

Current Required Additions

pH 7.2

pH 7.4

1.7 Litres Acid

Total Alkalinity 42ppm


9.0 kg Bicarb

Calcium Hardness 225ppm



Correct Way to ADD CHEMICALS to your Pool

Timing is everything

As the pH is already low and a NEGATIVE imbalance is occurring in the water, add the Bicarb by either mixing with water in a bucket, or straight from the package, but make sure you EVENLY distribute across the pool. And ideally with the pump running to help distribute the Bicarb.

Then approx 1 Hour LATER still whilst pump running adding the acid one liter at a time at one hourly interval.

Personal Notes

I realize this in some ways rejects claims and recommendations made out there in regards to the adding of Acid. Their recommendation is adding no more than 1 liter every 24 hours if required, and the two reasons for this:

  1. The acid is heavier than water and if poured directly into the pool where there is little water movement, it will settle to the bottom and etch out the plaster/cement and also have an adverse effect on the vinyl liner until it dissipates through the water.
  2. They don’t do sufficient testing and analyzing and planning of treatment before going ahead with the treatment.

- Hardy

Other Factors

Because we have used a scientific method of testing, analyzing tests, and planning the treatment before we begin, we know we have an Alkalinity high enough to absorb any excess acid which may be added.

Now if you (Customer) goes home and applies exactly what you have been told to do, then 95% of the time, the water will balance perfectly. The reason we say 95% of the time is because two things can occur in the following hours.

  • It may rain, changing the balance.
  • Make-up water may be added.
  • Debris ie: organic leaf matter and dust from local surroundings.

The above being a negative imbalance in the pool and to give you an example of what can happen to a marble sheen finished pool and why and how to overcome this situation when this occurs.

When the pool was initially filled with water, it was quite possible that the figures(Water Test) were to show:-

  • pH - 7.4
  • Total Alkalinity - 30ppm
  • Calcium Hardness - 50ppm


The above will give a VERY strong NEGATIVE imbalance.

The Poolman tested the water and made the pH ok, Total Alkalinity a bit low so he put in 5.0kg of Bicarb and the Alkalinity rose to between 90-100ppm and the pH to 7.8 however he did not know or worry about the pH rise.

Therefore the balance was still way out requiring a Calcium Hardness of 130-140 ppm to balance the water at 7.8 pH.

A couple of days later, the pool owner tests his pH as shown by the Pool/man he adds the acid to lower the 7.8 pH.

Now the pH is 7.4 and the Alkalinity down to approx 70ppm, the BALANCE is now way out because the Calcium Hardness now should be 450ppm.

Where can the water get Calcium?

The only place is the walls and floor of the pool structure. The calcium in the cement and marble render is made up of CALCIUM CARBONATES.

The cement comes out and leaves a rough surface and discolors on the pool surface.

Now let's look at a POSITIVE IMBALANCED pool and its correction.

  • Pool size - 45000 Litre.
  • pH - 7.6
  • Total Alkalinity - 540ppm
  • Calcium Hardness - 380ppm
  • A.D.R - 1 drop

Pool water with the above readings or close by is generally cloudy in nature.

Using the Langelier Index Chart run a straight line across the Total Alkalinity and Calcium Hardness readings, and it will show to have balanced water we need to have a pH of 6.7 This is way too LOW for swimming pools and will also contribute or promote the formation of Chloramines.

As before, use our Calcium reading as a set point and adjust accordingly.

With a straight line drawn through the optimum pH of 7.4, we will require a Total Alkalinity of 80ppm to obtain balanced water.

To correct the pool water we carry out the following:

Let's consider the A.D.R(Acid Demand) test which by referring to a chart tells us 0.3 liters of Hydrochloric Acid is needed. This will help matters slightly, however, will not give the drop required in Total Alkalinity. Consulting the Total Alkalinity Chart for lowering T/A using Acid.

Again, it all depends

We have to drop 460ppm so check the chart and it says seven liters per 100ppm required to drop. That is 32 Liters required to give us 80 ppm. CRAZY YOU SAY, No stop thinking about what was said, “IT ALL DEPENDS”.

In this pool you would find that the first 10 - 15 Litres would create NO pH change at all only on the last 5 liters would it begin to change the pH. The pH change would end up in the range of 6.0-6.5 and would be adjusted back up by doing another pH test and then the Base Demand Test and using a small amount of Soda Ash as indicated of the chart, and the figures would then end up like this:

  • pH 7.4 (Spot On)
  • Total Alkalinity 80 ppm (Good)
  • Calcium Hardness 380ppm (Spot On)
  • A Balanced Combination.


Another example

And to give you another example which should not be as expensive as the above scenario but still as tricky as the above and how you would approach a pool with the following readings.

  • pH 7.6
  • Total Alkalinity 540ppm
  • Calcium Hardness 380ppm
  •  Acid Demand ADR 1. Drop


Using the Langelier Index Chart see that the closer you can move both the Calcium and Total Alkalinity to the 180ppm figure the easier it will be to balance.

You will also notice that there is a very POSITIVE imbalance in the pool, thus this could be CLOUDY water.

Don't fight it, coax it

So instead of fighting the water, let’s help the water do what it wants to do which is rid of the dissolved solids in it.

Do the pH test again to check it is 7.6 and then a Base demand test drop by drop until an 8.3 reading is obtained. See it takes 2 Drops. Referring to the Chart it tells us 330gms of Soda Ash are needed to increase the pH to 8.3.

When the Soda Ash is Added an even greater imbalance is created and the water drives more solids out of solution into suspension thus forming dense clouding in the pool.

Now using a non pH Clarifier preferably anionic polymer to flocculate the suspended Calcium and bicarbonates.

When these settle to the bottom of the pool vacuum the pool to WASTE. ( Note: Don’t leave these salts on the floor too long in a marbled pool)

Other Situations

Now if the water is tested the results would be similar to the following if all was perfect:-

  • pH 8.3
  • Calcium Hardness 70ppm
  • Total Alkalinity 80ppm

It is hard to obtain this situation of perfect movement. The more possible situation would be:-

  • pH 8.3
  • Calcium Hardness 150ppm
  • Total Alkalinity 200ppm

To balance the above do an acid demand test on the 8.3 pH and come up with an addition of 1.0 Litre of Acid.

This will lower the pH to 7.4 and the Total Alkalinity by 10-15ppm. This will give us the readings as:-

  • pH 7.4
  • Calcium Hardness 150ppm
  • Total Alkalinity 190ppm

This will show a slight imbalance to the negative side now but will allow movement to balance up again with make-up water. This way you have obtained a balance with far less chemical addition than the standard method and have removed the solids physically from the water. Not just redissolved or changed their composition within the water.

In this process what has also been done is lowering the TDS level (Total Dissolved Solids) level without diluting the volume. This also is the only way to obtain lower Total dissolved Solids TDS.

Take the Scientific Approach

Take a scientific approach and execution in the tests and treatment. Always follow the system:

  1. Test
  2. Analyse
  3. Plan Treatment
  4. Treat.

Remember, IT ALL DEPENDS upon the three factors - pH, Total Alkalinity and Calcium Hardness and three minor factors temperature, TDS(Total Dissolved Solids), and stabilizer.

As I have tried to explain and mention, there are no real levels: as long as they are balanced then the water is easy to manage.

And many people are amazed when you say their pool needs 30kg of Bi-carb are needed for their pool water. But if that is what is required then that is how much must be used. However, if it is easier or more economical to raise the Calcium if Calcium Chloride(Hardness Increaser)is available, then use and raise the C/H to somewhere in the 120-170ppm range. This will reduce the amount of Bicarb needed because the Alkalinity will not have to be as high.

TDS or Total Dissolved Solids

First and Foremost: Total dissolved solids SHOULD NOT be confused with water balance.

Total dissolved solids (TDS) are the total of all minerals, metals, salts. Organic matter from our bodies or called phosphate etc which is dissolved in the water. Remember this does not include matter which is suspended in the water; it must be dissolved.

The biggest problems caused by an excess of TDS are the following:

  1. 1). Cloudiness of water, whereby the solids which we measured as Calcium Hardness and Total Alkalinity are high. When the pH rises and water becomes unbalanced and cloudiness occur.
  2. 2). Loss of efficiency of chlorination. This occurs because no more particles can dissolve which leaves suspended solids to surround bacteria and algae and stop the chlorine from getting near the pollution.
  3. Like if you have someone in trouble in the middle of the pool, they are the only person in the water so it is easy to rescue the person. Now if the pool was crowded with people, it would be very difficult to get to the person who is in trouble. This is the same problem Chlorine has.


With Spa Pools the chances of having a high TDS are far greater than those in large pools due to the high density of Organic pollution per unit of volume of water. This can lead to discoloration of the water, shorten filter cycles and expel bad smells, especially in heated Spa. The easiest way to controlling TDS in small Spas is to empty when the level rises above 900-1100ppm and refill.

Too low TDS can also cause problems, and by too low 400-500ppm. And with this reading, you can be fairly sure of also having a negative imbalance in the water.

Even though TDS and water balance are two different things they both tell the same story and point to problems in the water.

Major problems that tend to occur with too low TDS generally follow the pattern below:

Filtration Problems

Too low TDS will lead to problems in the filtration system. It has been discovered that although the filters remove only suspended solids NOT dissolved solids, the amount and the size of a certain suspended matter is related to the TDS, of the water containing it. As the water is lowered in TDS the particles which would normally adhere together and be large enough to be removed by the filtration system, stay apart and pass through, especially with Sand filters.

This has been proven where a filter would not remove the colour from pool water at a TDS of 50ppm, but when increased to 550ppm without chlorination the colour was reasonably removed.

Green-tinted pool

Low TDS will lead to a light green tinge appearing in the pool water as there is no body in the water to reflect the light and thus give the water a BLUE look colour. By increasing the TDS above 150-200ppm the colour will be removed even without filtration.

Chlorine usually removes colour by oxidizing the particles which are causing the colour and thus by eliminating to form salt in the water which in turn increases the TDS. Now if the water is green through lack of TDS or lack of body also called the lack of the ability of the water to reflect, then the chlorine cannot be expected to work on something which does not exist. ONLY if there is some mineral or organic matter dissolved or suspended in water can the chlorine remove the colour to achieve this TDS levels must be in the range of 500-800ppm.


Why Chlorinate?

Swimming Pools are damp and warm by nature, a breeding ground for bacteria, algae, and many other organic compounds.

Not all are harmful, but those which are, usually outnumber those unharmful ones.

Whilst swimming a lot of bacteria, dirt, germs, body oils, skin, and other body secretions into the pool water called either phosphate or pollution and when this increases in the water it tends to change the colour, taste, and an unpleasant odor, and all this can be removed with chlorination.

When Chlorine is added to the pool, it reacts with ammonia compounds which are present in the form of urine and body perspiration and forms what are known as Chloramines, which are also removed with more Chlorine.

Chlorination also kills all bacteria and germs and reduces them to dead organic matter, it will then oxidize the organic matter into NOTHINGNESS, thus not only killing unwanted live organisms in the water but totally removes them.

The benefits gained from chlorination:

  • Less vacuuming of the pool
  • Longer filter life
  • Less backwashing
  • A cleaner and safer pool

Calcium Hypochlorite would be the largest being used in Australia, and when this product is added to water we have the following reaction:

Calcium Hypochlorite(Dry)   Water   Hypochlorous Acid Calcium Hydroxide

Ca(OCl)+H20 =2HOCl + Ca(OH)2

So when they combine, there is Hypochlorous acid formed and this is the major ingredient in killing the bacteria, algae and oxidizing the organic matter, removal of colour and taste, and the destruction of what are called chloramines. In this process at the same time a small amount of Calcium Hydroxide is formed which over some time will gradually raise the pH of the water; thus the need to test for pH occasionally and adjust using acid.

Chlorine and its relation to pH

Most Calcium Hypochlorite sold and used today contains a strength varying from 60-80% Chlorine which forms into hypochlorous acid. This acid is the FREE available chlorine. Therefore, it is needed to be known what percentage of available chlorine is in the Chlorine compound being used. There is one other reaction happening in the pool known as ionization, this occurs when all compounds are mixed in the water as it does when hypochlorous acid is formed.

The HOCL breaks up to form H+ or positive hydrogen ions and OCL or negative hypochlorite ions. This is also a reversible reaction.

All the hypochlorous Acid we have made in that reaction may be no more. It may have become what we call in the industry “disassociated”. And chlorine in a “disassociated” form, is as good as useless. The best and most practical way to control this problem is by controlling the pH.


The lower the pH the greater the amount of Hypochlorous acid in an undissociated form and the less hypochlorite ion. The higher the pH, the less hypochlorous acid and the greater hypochlorite ions.

Now water needs to be at a comfortable pH for people to swim in ranging from 7.2-7.6.

There is now a supply of available hypochlorous acid ranging from approx, 60% at 7.2 to 40% at 7.6. This the most that can be obtained and the best must be done with it. Work on the basis that efficient chlorination is to obtain the most amount of hypochlorous acid possible at a time when there will be the least reaction with sunlight.

As mentioned, chlorine in the hypochlorous acid form breaks down bacteria and algae. It does this by eating into the very basis of any living organism- it’s enzymes. Once the enzymes in the living substance are destroyed, then the organism can no longer live; so bacteria and algae die. The other problem which can occur with algae and that is dead algae forms a coating over the live algae underneath and STOPS any further action from the chlorine.


Adding chlorine to such an extent that the chlorine oxidizes and destroys the dead algae allowing the chlorine to work on any live algae underneath.

Public Pools

The best way to explain this is to talk about a pool that has continual chlorination such as a council pool.

When the pool is opened in the morning, the water is crystal clear, no algae, bacteria or objectionable compounds in the water-just as much hypochlorous acid as the pH will permit. In the process of people swimming a lot of pollution is brought into the pool in the form of perspiration, urine, and body excretions all contain strong compounds such as ammonia. The ammonia combines with chlorine to form what we call monochloramines. Once there is enough ammonia, it can react to dichloramines and trichloramine.

It is the nitrogen trichloride along with the di and mono chloramines which give people sore eyes, smell and taste of chlorine in pools. As more people swim, more ammonia is introduced and thus more chloramines. Chlorine does a tremendous job breaking these chloramines down and getting rid of all the above nasties as long as there is ENOUGH FREE CHLORINE present and available.

A public pool like above has continuous chlorination and therefore continual build up and breakdown of chloramines.

Private Pools

A private Home Swimming pool, has a large build up of nitrogenous compounds or ammonia during the day when people are using the pool. As soon as chlorine is introduced at night, there will be extremely fast growth of chloramines as the free chlorine combines with the ammonia compounds.

Let me define the two products being discussed:

  • Hypochlorous acid which is known as Free Available Chlorine. This means it is free to work when and as required to kill bacteria and algae, oxidize organic material and breakdown chlorine or chloramine compounds. This Chlorine is known as FAC(Free available chlorine) and it is the most valuable asset in treating your pool water.
  • Chloramines, due to the large amount of chlorine they contain, have a very weak effect(but some effect) on killing bacteria, algae and oxidizing organic material. This chlorine which is not free to work as it please, is known as COMBINED AVAILABLE CHLORINE or CAC. As chlorine, it is basically useless and affects the eyes, taste and smell and uses the FAC(Free available chlorine) instead of leaving it for more important tasks.

The above two products give us the “Total Available Chlorine” or TAC- the sum of the FAC and combined chlorines. The test we should do on the pools water are most easily done on FAC(Free available chlorine) and TAC(Total available chlorine) subtract the FAC from the TAC to receive a measure on the CAC(Combined available chlorine)

Testing For Chlorine

Most common today is DPD or utilizes the use of tablets or drops which dissolve once placed in a sample. The benefit of the DPD system is that the exact volume of a tablet of a specific designation is added to the sample(Firstly a No#1 tablet) and when it dissolves it gives an exact reading of the FAC, in other words, a true and accurate reading of the chlorine which is free and available.

Next we add a No#3 tablet to the same sample and if chlorination is correct, no colour change. However if there are chloramines present, then they will show by darkening the colour of the sample. This immediately tells us if we have correct or incorrect chlorination and how to then take remedial action.

Update: There are now more convenient ways of testing pool water like the Water TechniX 7-in-1 Pool Test Strips

Breakpoint chlorination means chlorinating to a level whereby when testing the FAC (Free avail Chlor) and the TAC(total avail Chlor) at a future time, the exact same answers for both tests. This means that however much chlorine was added, it is enough to kill all bacteria and algae, oxidize all the organic materials and destroy all chloramines which would have been formed when added, only then will it be considered water sfe and clean enough for you to swim in.

Breakpoint Chlorination


How much chlorine is needed to overcome all the pollution in the water. For this, an initial 5.0 mg/l chlorine level is needed in the water. Remember there is a disadvantage because everyone has been swimming in the pool all day and there is no chlorine, so one can not do a chlorine test to check the CAC (Combined Avail Chlor) to tell how much chlorine is needed to break the CAC down.

All that can be done is to correct the pH to 7.2-7.6 level and add the required amount of chlorine for 5 mg/l level as per chart.

Mg/l(definition)- mg/l means the number of milligrams of a product in a liter or kilogram of water - thus 5 mg/l means 5 milligrams in one liter or 0.225 kg in 45,000 liters.

However, this is if the product is 100% pure compound and that being used is only 65%, so add (225 gms divided by 0.65) being 350 grams.

Types of Chlorine

Calcium Hypochlorite or Cal-Hypo

 This chlorine compound generally comes in a strength of 65% to 77% and the remainder are impurities into which the chlorine is fused, there is also a certain amount of water retained. As soon as this chemical is released in the water hypochlorous acid is formed to the entire amount of chlorine inserted. This acid then ionizes according to what the pH is and what is left in the form of hypochlorous acid, immediately goes to work at its full strength to kill bacteria and algae.

Note: as soon as sunlight is focused on the water, approx ⅓ of the FAC is lost to sunlight.

As there is no addition of chlorine continuously, then the loss of ⅓ of the ⅔ left and so on until there is no more left. Thus more Calcium Hypochlorite must be added in the evening, also due to its instantaneous reactions at full strength, it is a very advisable product to use, especially in the removal of algae and the removal of Chloramines from the pool water.

Stabilized Chlorine or Sodium DichloroIsoCyanurate

This is usually in a fine powder form and contains 3 major components.

56% Chlorine, 40% Cyanuric acid(before Hydrolysis in water), 4% Sodium

The reason for using a stabilizer is to allow only a certain amount of hypochlorous acid to form at any one time, thus only allowing a small percentage for the sun to remove its third form. Therefore, the total loss of chlorine to the sun is far less than with Calcium Hypochlorite where it all forms hypochlorous acid at any time.

Pools using Stabilized chlorine have to use a product similar to calcium hypochlorite known as “Shockout” which is basically calcium hypo which oxidises out all organic matter which the normally used chlorine has not been able to remove.

It must be remembered that as each dose of chlorine is added, approximately one third of the dose is cyanuric acid which continues to build up in the pool water and further retards the availability of the hypochlorous acid from stabilized chlorine.

Sodium Trichloro Iso Cyanurate or Tri-Chlor

This sanitiser is usually made in a tablet form and used in dispensers and feeders.

Made of: 89% Chlorine, 7% Cyanuric acid (before hydrolysis), 4% Sodium

This is very similar to Dichlor except we have a greater volume of chlorine and a lesser volume of cyanuric acid.

The way these work on a double release principale of releasing a certain percentage into the water as the tablet dissolves and the cyanuric acid controls the hypochlorous acid release once the chlorine is in the pool.

The biggest benefit of using Stabilized Chlorine is that the impurities are lower in volume and do not have a residue on the floor of the pool. It also allows for FAC levels to be present at all times.

Salt water chlorination

This is a process where Salt has been added to the pool water, and most Chlorinators these days work between salt levels of approximately 4000-6000ppm as the water passes through the Salt CELL(metal plates) which have a negative and positive discharge controlled by the chlorinator, as the salt combines with the water and becomes an electrolyte eg: losing some of its molecular bond and forming Na++ ions and Cl` ions. These ions allow the transfer of a small charge of current to occur across the metal electrodes in the Salt Cell and in this process Sodium Hypochlorite is produced.

Salt water Chlorination today is the most common and easiest form used to sanitize the pool.

The biggest thing I have found is Chlorinator NOT correctly sized to the pool encompassing all the unforeseen from pollution to bathing loads and sun. Also on many occasions chlorine out-put is only sitting at 20% and the other main issue is too low salt level.

Chlorination Notes

Salt Water Chlorination

When the chlorinator is running at 80% there should be a constant mist coming off the salt cell, and check to see the plates are not worn.

People forget they must still check and correct the pH level at least once a week and Total Alkalinity and calcium hardness monthly, and ensure the out-put is correct.

When an automatic dosage machine be it a chlorinator or liquid dosing system feeding into the piping, take care to ensure the return to the pool inlets(Return) are min 300mm-450mm below water level, the deeper the better, and turned towards the base of the pool to force heavily chlorinated water to the main body of water before it has a chance to dissipate into the air.

 And with any Sanitisation system, the best time to run them as much as possible is at NIGHT when there is NO sun to dissipate the chlorine as it enters the pool.


When using Calcium Hypochlorite(Hypo) or granular chlorines, the only time to have a fixed chlorine level to work to and for, is when doing an early morning test-thus one must dose accordingly.

 A test of 0.5ppm of FAC(Free available chlorine) with a CAC (Combined available chlorine) of 0.0 is acceptable, as mentioned earlier there must be no CAC at this test time but still have a FAC. Then the chlorine has done its work in killing all bacteria and oxidizing organic compounds and removed all the CAC. NOW you have perfect water to swim in.


Stabilised Chlorine

When Stabilised Chlorine is used, the FAC must be higher at all times because it only needs the introduction of a small amount of pollution and there is no more FAC. Admittedly there will be more FAC building up during the day but as there is no shock dosing nightly, try to stay ahead.

If working with a 30ppm Cyanuric(Stabilizer) Level, then run a minimum FAC of 1.0-1.5ppm. The higher the Stabilizer reading the higher minimum FAC, But remember the higher the Stabilizer generally also increases the TDS(Total Dissolved Solids) which will impede the processes of the chlorine.

Very Important notes with regard to Chlorine and Chlorination

 Very few problems occur whilst using Chlorine, but they can occur:

  • If chlorine is added to the water when the pH is exceedingly low, the water may turn GREEN or BROWN. If it turns green, copper is present in the water and has been oxidized out of solution. If brown, usually iron has been oxidized to form Ferric Oxide which settles to the bottom of the pool.

  • It’s usually found that the pH is in the low 6.0 or even lower. Using the Base demand test, calculate the soda ash required to increase the pH to 7.4. Then test for Alkalinity and Calcium Hardness as well- the alkalinity has probably been dropped by the low pH. Recorrect and balance the water, add chlorine, and the water will colour back to blue.

  • Cloudiness caused by lack of chlorination, when using stabilizer based chlorine, where the chlorine will not form hypochlorous acid or the chlorine level being held relative to the stabilizer level is not high enough. The pool water will cloud, being caused by the excess organic material in the water which is no longer being oxidized out of the Water.

  •  In most cases it just needs a good superchlorination to at least 25mg/l to just get rid of the current CAC as well as today's addition.

  • Don't be scared to add 2kg two kilos of chlorine to shock the pool. It will not hurt anything, but will clear the water.

  • Chlorine can also be used to remove staining on pool floors by direct application of Calcium Hypochlorite, it is also the best method for removal of algae.

  • NEVER MIX CHEMICALS, whether they be two chlorines or chlorine and another product- NO IFS, NO BUTS, NEVER NEVER add water to chlorine or chemicals in general, always add the chlorine, chemical to water, never vice versa.

  •  Try NOT to keep chlorine in the same shed as oils or brake fluid or petrol or it’s derivatives. And never store Calcium Hypo and Cyanurates in the same closed environment and if anything keep them as far as possible as the combination of fumes given off in a moist atmosphere can cause instantaneous combustion

- Hardy

Chlorination FAQs

Q: How soon after adding chlorine can you swim ?

A: The pool requires levels of chlorine 20ppm or higher to cause eye irritation so unless you are shock dosing for a reason, swimming can start in 30.min.

Q: Why Chlorinate every day ?

A: By daily Chlorinating the buildup of chloramines and bacteria never gets high which can’t be removed by a reasonable dosage of chlorine.

Q: How much chlorine should be used ?

A: Well you do need to work out the volume of the pool, and do a chlorine test and remember what type of chlorine ? Cal Hypo(Strength 77%), or Sodium Hypo(13%) and don’t assume or estimate “a cupful”.

Q:hen should one put chlorine in the pool.?

A: In the evening because this gives the hypochlorous acid a chance to work without losing its effectiveness to the sun.

Q: Why does one get so much residue on the floor of the pool.?

A: This is usually because the water balance is out and not necessarily the fault of the chlorine. Usually the water is on the positive side and will NOT absorb the calcium or sodium from the chlorine. Correct water balance, and vac the pool once a week will ensure less residue.

Q: When should one test for Chlorine ?

A: Depending on the Chlorine being used if it is a Hypo test in the morning - 0.5 mg/l FAC(Free avail Chlor) reading should be registered. If using Di or Tri Chlorine, tests can done anytime of the day and the reading must always be 1.0-1.5 mg/l FAC at 30ppm Stabilizer level.

Algae Control

What is Algae?

Algae are chlorophyll containing plants without true roots and without distinction of leaves or stems.

Algae needs energy from the sun to convert inorganic matter into their own protoplasm. They do not require oxygen to live: they actually split up water to produce oxygen. This is why they are so good in harbouring aerobic bacteria which live on the oxygen produced by algae.

Also, undissolved chemical deposits such as Calcium deposits on walls and floors of pools give growth areas to algae.

Why is Algae Control Important?

Algae in the swimming pool causes staining and slippery conditions and shows that the chlorination of the pool is defective. Any pool which has the correct pH, water balance and an adequate amount of FAC(Free avail Chlor) will NOT contain Algae. Algae growths will always have a greater chance of growing in water with a higher mineral content or high Total dissolved solids level. In the presence of sunlight the inorganic mineral compounds dissolved in the water become the chemical building blocks with which the algae make the cells to form their bodies.

Algae is unslightly and unhealthy

Algae is not healthy and also very unsightly. Its presence means the pool has been neglected, many people claim that even when they keep good chlorine levels (according to their test kit which may only be giving TAC, and their pH is correct, they still have algae.! This is usually too good to be true, as mentioned before, it is rare to find algae in a pool which does not have deposits, so if it does have deposits that means the pool has or is not balanced for a while.

The easiest method of eradication of algae is to prevent it in the first place. The work of the chlorine can be helped by algaecides. The main one being used for a long time was copper sulphate. However this has proved to be troublesome due to the deposits of copper occurring on the walls and floor and a slow build-up of sulphuric acid.

Two main types of algaecide:

  • Quaternary ammonium compounds which tend to soften the water and chemically destroy any algae spore as it forms.
  • Cationic polymers which form two functions. As wetting agents they envelop the algae spore and suffocate it and secondly, they react with negative ions in the water, in other words clarifies(flocculating effect) the water which drops to the floor to be vacuumed to waste.


Step-by-step Algaecide application:

  • Lower the pH to 6.8 - this has two benefits.
    • When the chlorine is added, the percentage of hypochlorous acid is very high, which is what kills everything.
    • When the chlorine is low or removed, the low pH will dissolve the deposits upon which algae is growing.
  • Next add the algaecide which can be used on the following basis:
    • 5 Liters/45000 Quaternary ammonia.
    • 1 Liter /45000 Cationic polymer
  • Then superchlorinate for algae removal. For the 45000 litre pool, this would be 1.7kg of 65% Hypo.
  • Let this react overnight and then brush the affected area.
  • Repeat the chlorine addition and the brushing until the algae disappears.
  • The reason for brushing is because as algae dies, it forms a seal/layer over the live algae underneath, thus not allowing the present chlorine to eradicate it.
  • Should this not work in the affected area, acid washing by applying a neat solution of 30% Hydrochloric Acid be sprayed or brushed on the affected area.
    • When acid washing, be sure to wear protective clothing, rubber gloves and eye protection.


Algae also changes its growth patterns according to the water temperature, therefore as summer approaches the temperature rises, so does the chance of algae growth. Therefore, chlorine dosage must increase as the temperature increases.