Mr Pool Man's A-Z of Pool Terminology

An Above ground pool is a swimming pool that is located, well, above ground. Above ground pools are usually made with vinyl liners with the pool surfaces and walls located above ground.

The absolute filter rating is a rating that indicates that 99.9% of particles larger than the stated size will be trapped by the filter while operating under nominal conditions.

Pool Accessories are basically the "non-essential" equipment for your pool. Although they're not essential, they make pool life easier for everyone involved in the care and maintenance of your pool. If you're looking for pool accessories, then Mr Pool Man is your online pool shop of choice in Australia.

Acid is used to lower your pool's total pH Level. A high acid level (read as low pH) can cause corrosion on your pool surfaces and equipment. Acidic water can also cause skin irritation. To lower your pool water's pH levels without handling liquid acid, you can opt to use pH Down tablets.

Acid demand is a reading in many reagent test kits that determines the amount of acid required to reduce your pool's pH levels to their recommended levels.

Acid washing is a method used to "strip" a thin layer of your pool surface to remove mineral deposits and deeply rooted stains. Acid washing should be done by a pool professional since a full drain of the pool is required. If you're the DIY-type of person, you can opt to do a no-drain acid wash.

Typically located at the top of cartridge filters or sand filters just beside the pressure gauge, the air relief valve allows you to vent or release air that is trapped within your filter unit.

This is an optional accessory that's used to inject air into your spa's return jets. What's a spa without bubbles right?

Every pool owner knows what algae is. There are thousands of species of algae that may infest your pool and they come in a variety of colors from yellow, green, brown, and every other shade in-between. This is a living organism that is easily combatted by proper application of pool chlorine. If you're faced with an algae bloom or by green pool water, check out our guide on how to deal with green pool water here.

Algaecide is typically used to control, you guessed it, algae. If your pool chlorine levels are properly maintained then you usually won't need algaecide, but it's good practice to dose your pool monthly with some long life algaecide as a preventative. (Peace of mind = priceless)

Alkalinity Increasers or what we carry as Alkalinity Up on our online pool shop is a chemical that is added to your pool to increase your pool's alkalinity levels whenever they drop below 80ppm. Alkalinity plays an important role in your pool's pH, which in turn affects your chlorine performance. For more information on the relationship of pH and chlorine, check out this helpful article here.

While it may sound exotic, alternative pool sanitisers are just ways of sanitising your pool without using traditional pool chlorine or bromine. Alternative pool sanitisers can include salt water chlorinators, mineral pool systems, magnapool systems and the like.

Most commercial flocculants are made with Aluminum Sulfate or "alum" for short. These work by drawing in tiny microscopic particles in your pool that are too fine to be filtered out, clumping them together making them sink to the bottom of your pool.

Automatic pool cleaners are basically what the name implies. They automatically clean your pool for you. There are three main categories of automatic pool cleaners, namely pressure-side pool cleaners, suction pool cleaners, and robotic pool cleaners. 

Backwashing is the process in which your sand or DE filter is filled with water in reverse, loosening up any trapped dirt and debris before being flushed out of your filtration system. See our comprehensive backwashing guide here for more details.

Bacteria, unlike algae that's basically a pool nuisance, can cause many water-borne diseases and have to be controlled/destroyed as soon as possible. The way this can be achieved is to keep your pool chlorine levels at their optimal levels which is at 1-3ppm or install a salt water chlorinator to constantly dose your pool with chlorine.

Balanced pool water simply means that all of your pool chemical levels are at their optimal levels. For more information on what pool chemicals do, check out Mr Pool Man's Ultimate Guide to Pool Chemicals.

A "base" is basically the opposite of your acid. Base chemicals are basically your alkalinity raising chemicals that counteract and neutralize acids.

Much like your acid demand, a base demand simply indicates how much alkalinity raising chemicals are needed to raise the pH towards neutral levels.

Bather load is basically the number of people using your pool. A normal bathing load is you and your family, normally using the pool. A high bather load is when you have guests over or when there are more people using the pool than normal.

An algae bloom is when suspended algae particles "bloom" and turns your crystal clear pool water into a murky green swamp. Algae blooms can be prevented by keeping your chlorine levels at 1-3ppm and with a monthly application of algaecide and phosphate removers.

Booster pumps are separate from your pool pump. They are usually used to power pressure-side pool cleaners like the ones from Polaris which require a bit of pressure to operate properly.

Breakpoint Chlorination is when your chlorine levels reach a level where they oxidise all of the chloramines in your pool. This is usually 10 times the amount of Total Chlorine in your pool. For more details on Breakpoint or Breakeven Chlorination, you can check out our comprehensive guide here.

BTU stands for British Thermal Unit, this is the unit of heating used in Gas-fired appliances, cooking ranges, and of course, gas powered pool heaters.

A bucket test is a DIY testing method for determining if your pool has a leak or not. We have a full guide on how to determine if your pool has a leak (which includes doing the bucket test) which you can check out right here.

Also linked to your Total alkalinity levels, buffer prevents wide swings in your pool's pH levels.  

Calcium Hardness is the calcium level in your pool. Water will naturally find its "level" if the calcium levels in your pool are low, the water will look for a source of calcium to supplement its requirement and it will "eat" the calcium from your pool surfaces, causing corrosion. If the level is too high, then water will "spit" out the excess calcium, causing scale and calcium deposits on your pool surfaces.

The active ingredient in many Calcium Up pool chemical products, used to raise the calcium hardness levels in your pool.

A type of chlorine that's granular. Often used as pool shock. Usually comes with 65% chlorine content or 73%, depending on the manufacturer.

Capacitors, or more specifically pool pump capacitors help your pool impeller reach it's optimal operating speed much faster. A broken capacitor is usually the cause for your pool pump "humming" but not spinning when it's turned on. Mr Pool Man has a wide range of capacitors available for the most popular pump sizes in Australia, be sure to consult your owner's manual for the correct model before ordering.

Filter Cartridge or just Cartridge is a replacement filter element for your cartridge filters. Be sure to correctly measure your existing cartridge filter to get the exact model for your cartridge filter unit.

Not to be confused with filter cartridges, a cartridge filter is the filtration unit itself and not the element inside. Cartridge filters use cartridges that are made with fibrous material that's pleated and in more cases more effective than sand filters. Mr Pool Man has one of the widest selections of cartridge filters online in Australia so be sure to check out our selection of cartridge filters here.

In Pool Man speak, cavitation happens when your pump is oversized and water flows into your pump too fast, creating pockets of air and making it appear that your pump isn't primed. This is one of the dangers of having too big a pool pump for your pipes. Cavitation can damage your pool pump and corrode the surrounding pipes and fittings in your pool system.

Channeling is a phenomenon that happens in sand filter where the flow of water creates a "channel" in your sand, leaving the water unfiltered as it passes through your sand filter. Channeling is usually caused by an oversized pool pump or if your sand filter elements are gunked up or if there's a build up of calcium in your pool filter sand. Channeling can be fixed with a good backwash or manually hosing out the inside of your sand filter with a garden hose. If your channelling is caused by an oversized pool pump then the only way to prevent this is to either change your pump to something smaller or to change your filter to something bigger.

A Check valve is a pipe fitting that only allows water to flow in one direction. Very helpful in preventing backflow of water.

A chemical feeder is any type of pool accessory that automatically dispenses chemicals in your pool. These can be as simple as a floating chlorine puck dispensers to probe-controlled automatic chemical dispensers like the Rola Chem chemical dispensers.

Chloramines are the combined chlorine your pool. This causes the "pool chlorine" smell in your pool and is a sign of having insufficient chlorine in your pool. To remove minor levels of chloramines, shocking is usually enough, but once you reach high levels of combined chlorine, you may need to reach breakpoint chlorination or break a chlorine lock.

This is probably the single most important pool chemical on can have in their arsenal. Too low a chlorine level and you're leaving yourself open to algae blooms other contaminants in your pool and too high a level can cause skin and eye irritation. For more information on pool chlorine, check out our pool chemical focus on chlorine here.

While this term isn't widely used by home pool owners, it's still best to know what it means so we won't be left in the dark the next time someone mentions it. Chlorine demand is basically the amount of chlorine that is used in the process of sanitising your pool. To make it easy to understand, the dirtier your pool, the higher the chlorine demand, it's as simple as that. So when you hear someone say that their pool has a high chlorine demand, that basically means that their pool is dirty!

A chlorine generator is simply another name for a Salt Water Chlorinator.

Chlorine shock is basically just your liquid or granular chlorine without any form of stabiliser added to it and usually has higher chlorine content. Shock is usually used to quickly raise the chlorine levels in your pool to destroy chloramines and to deal with algae blooms and other contaminant problems.

These are "milder" versions of flocculants and are used to help your pool filter system clear out your pool water. For more information on the differences between clarifiers and flocculants, check out our Clarifiers VS Flocculant article here.

Closing your pool basically means that you're preparing your pool for extended periods of non-usage. Depending on your area, closing your pool can simply mean changing your pool maintenance routine to the absolute minimum, but for colder areas, we'll need to winterize our pool. For more information on winterizing your pool, see our complete winterizing your pool guide here.

Although cloudy pool water sounds self-explanatory, there are a lot of causes for pool water cloudiness. Cloudy pool water can be caused by a chemical imablance, high calcium levels, algae blooms or insufficient filtration. To determine the actual cause of cloudy pool water, it's good to test your pool chemical levels.

Combined Chlorine is just another term for Chloramines, see above for more information on Chloramines.

A pool conditioner is another name pool guys use to protect your pool chlorine from UV rays. Sound familiar? It should! This is basically cyanuric acid, UV Blockout, or pool chlorine stabiliser!

This is the edge or the "lip" of an in-ground pool or spa.

Pool covers protect your pool from debris when not in use. It also helps reduce water evaporation and helps retain heat in your pools. It is the single most effective means in reducing expenses related to pool heating. For more information, check out our ultimate guide to pool covers here.

Cyanuric Acid or UV Blockout protects your pool chlorine from getting burned up by the sun's UV rays before it gets a chance to sanitise your pool. It's also important to ensure that you don't have too much cyanuric acid/stabiliser/conditioner in your pool as not to reduce the efficiency of your pool chlorine. For an in-depth look at cyanuric acid, check out our chemical spotlight on stabilisers here.

The pool deck is the immediate area around your pool. Thhis can be made out of stones, concrete, or even wood! While not a part of the pool itself, the deck design can greatly influence the look and feel of the atmosphere in your little own backyard paradise.

Commonly used in areas around indoor heated spas, dehumidifiers protect the room from excess humidity by sucking in all of the excess humidity in the air before it dampens everything in the room.

Diatomaceous Earth, let's just call it DE for simplicity's sake, is the filter element used in DE filters. This is made from the fossilised remains of tiny aquatic animals called diatoms. When it comes to filtration capability, nothing beats the crystal clear water that's produced by DE filters. The downside is that DE filters are the most demanding and expensive when it comes to the different home pool filtration systems.  

Another term for pool santising. The main chemical used to disinfect your pool is, you guessed it, pool chlorine.

This is the most consistent and accurate form of pool testing available out there. There are four common DPD reagents used in pools in Australia and around the world.

• DPD 1 measures free available chlorine
• DPD 2 (use with DPD 1) measures combined chlorine
• DPD 3 (use with DPD 1) measures total chlorine
• DPD 4 measures total available chlorine

One of the most common pool heating solutions, electric heaters use up a lot of energy to heat up your pool water. People are slowly switching to more energy-efficient pool heat pumps to save money on their pool heating bills.

A pipe fitting used to provide "turns" in your piping system. Usually comes in 45 degree and 90 degree aangles.

While uncommon in home pool use, enzymes are commonly used to break down organic debris and oils in pools.

A natural occurence where water escapes the pool. This is the number one cause of pool water and pool chemical loss. This loss can be prevented by the use of a good quality pool cover.

The expansion joint is the gap (usually 1 inch) between your pool's coping and your pool deck. This allows the pool to shift when it expands or contracts due to weather swings or when the cement "breathes".

There are three kinds of pool filters, sand filters, cartridge filters, and DE filters. Each type of filter have their own advantages and disadvantages which you can see here.

A filter cartridge is the filter element used by cartridge filters. There are genuine filter cartridges and replacement filter cartridges available on our online store. Are replacement filter cartridges worth it? Check out our OEM vs Genuine parts post here.

Not to be confused with filter cartridges, a filter grid is used in DE filters to hold in the DE Powder.

Often used as a last resort or when pool cloudiness is out of control, flocculants bind with loose particles in your pool and cause them to sink to the bottom, making them easier to vacuum out. Note: it is not recommended to use flocculants with cartridge filter systems.

There are three chlorine readings when testing your pool, "Total", "Combined", and "Free". The Free Chlorine reading determines the amount of available pool chlorine in your pool that is "active" in sanitising your pool water.

The amount of water flowing through a certain point (usually measured at the pump). Measured in GPM (gallons per minute) or LPM (Litres per minute).

A gasket is a type of mechanical seal that which fills the space between two surfaces and creates a seal or prevent leakage. A good example of a gasket is a spider gasket that's used on our multiport valves. If you have problems with your multiport, you can check out our multiport maintenance guide here.

Grout is typically a mixture of water, cement and sand and is usually used to fill in gaps, especially between tiles.

Also known as shotcrete, is concrete that's sprayed out of a hose and is typically used in pool construction and other applications requiring dense and hard concrete.

Also known as geothermal heat pumps, these are rarely used in home applications. These utilize the heat of the earth to heat up pool water.

A gate valve is basically an "on" and "off" switch for your water. Shut it off to completely restrict the flow of water and open it up to allow the flow of water through the pipes.

One of the earlier (and most popular) pool lighting options. They tend to run hot, consume a lot of electricity and require replacement every couple of years as they have a limited lifespan (burnout). They're slowly being replaced by energy efficient LED pool lighting systems due.

This is the term used for water with high calcium levels. If you live in an area where you get hard water from the tap, stock up on some Calcium Remover to properly regulate the calcium levels in your pool.

See "Calcium Hardness" entry above.

A pool heat pump draws in heat from the atmosphere and transfers it to your pool water, warming it up. These are very energy efficient and can warm your pool on cents on the dollar when compared with traditional electric and gas heaters. Click here for the benefits of using a pool heat pump.

There are three main types of pool heaters. The most common ones are gas and electric pool heaters. The newest types, pool heat pumps, are a little bit more expensive, but they pay for themselves in the long run through electricity savings.

Hot tubs and spas can be used interchangeably. These are usually stand alone units with their own filtration and pumping systems.

Hydrotherapy or "Water Cure" involves using your pool or spa for mild exercises and warmth. This helps relieve symptoms related to arthritis and other joint and muscular conditions.  

The impeller is responsible for creating the suction power in your pool pumps. Mr Pool Man carries a wide variety of impellers in our online shop for a wide variety of pool pumps.

The opposite of above ground pools, in ground pools are built entirely below ground level. They're the most expensive types of pools to build, but they're the most durable and they add considerable value to a home.

Inifity Pools are basically pools that are built to "blend in" with the natural scenery that usually includes oceans or other bodies of water. The visual illusion is that the pool goes on "until infinity". Click to see other swimming pool features that will make you go “wow.”

Return jets (usually equipped with eyeballs) is where filtered water flows back into the pool. Eyeballs are attached to direct the flow of the water to aid in circulation.

A very popular brand (Jandy) of two and three-way valves commonly used in pool plumbing applications.

Pool accessories typically made out of stainless steel designed to help you get in and out of the pool easier. Mr Pool Man carries marine-grade (only the best) pool ladders and rails on its online shop. Check out our collection of pool ladders and rails from S.R. Smith here.

The LSI or Langelier Saturation index tells you the state of your water. Water will always try to go back to its normal state. In a nutshell, high LSI values will cause scaling in your pool and a low LSI will be corrosive to your pool. The formula for determining the LSI value fo our pool is pH + Temperature Index + Calcium Index + Alkalinity Index – TDS index.

For more in-depth information on LSI, check out this LSI guide.

Three different pool cleaning accessories all designed to remove leaves from your pool.

• Leaf Skimmers - The smallest, lightest, and most agile of the three types of leaf removers. This accessory is perfect for floating leaves and debris and is the easiest to handle, very agile.
• Leaf Rakes - This accessory is a cross between leaf skimmers and leaf shovels. It has medium capacity and can be used to remove floating debris and those that sink to the bottom.
• Leaf Shovels - The biggest sized leaf remover with the largest bag. This is a bit bulky to use and is excellent for heavy debris.

Leaf Canisters are attachments for suction pool cleaners designed to trap leaves before they get sucked into your skimmers / pumping system while cleaning your pool with suction pool cleaners. The Water TechniX leaf canisters cost a fraction of the cost of other branded leaf canisters and they're just as durable and function the same!

A pool liner is basically what holds the water in the pool in Vinyl Pools (also known as Vinyl Liner Pools). These can easily be replaced over the weekend but they're also not as durable as fiberglass or concrete/gunite pools.

LED Pool lights are the latest and greatest in pool lighting technology. They consume far less energy than their traditional flourescent or incandescent lighting counterparts. They also last longer with rated lifespans of up to 30,000 hours. Mr Pool Man carries some of the best LED Pool Light brands in Australia, check out our online store for more information.

These are special types of in-ground swimming pools where the water level is perfectly level with the surrounding pool deck.

These are an alternative to salt water pools, instead of using salt, magnesium minerals are used to generate the chlorine for your pool using a salt & mineral chlorinator. This results in a much "silkier" water feel and may have other health benefits. For more information on mineral pools, check out our Magnapools: Hype or Hope post.

Mesh pool covers are cheaper alternatives to thicker pool covers. They're fairly easy to install and they protect your pool from debris. Mesh pool covers do not protect your pool from UV rays and evaporation.

Very expensive to install but if money is not an object, it's something worth considering when constructing a pool. Moving floors allow you to raise or lower your pool floor to adjust the depth or even completely hide your pool if you need the space for large gatherings or parties.

Natural Pools or Naked Pools use a special ioniser to sanitise the pool. These types of pool use minimum (or no) chemicals to maintain and may be a good option for those with extra sensitive skin. Learn more about Natural Pools and Naked Pools in our post entitled "The Naked Pool System: Baring it all out"

Opening your pool is basically getting your pool ready for usage afer a long period of disuse (usually over winter or during off-season) Opening your pool involves more than just throwing the covers off and jumping in. We have an in-depth guide for opening your pool which your can refer to here.

O-rings are used to seal in the space in between two or more parts. They're designed to compress and create an air and water tight seal. In pool applications, you can find O-rings on your pump lids, cartridge filter lids, pump body lids, and unions. Remember to always grease your O-rings with silicon based lubricants whenever they're accessed/exposed to air.

NEVER USE OIL-BASED LUBRICANTS on your O-rings.

While not really common, off-line chlorinators are used when inline chlorinators can't fit into the existing plumbing lines. Off-line chlorinators are usually plumbed in-between the pump and the filter, creating a path before being plumbed into the return lines, skipping the filter altogether.

This is an accessory that is usually attached to spas and hot tubs. These greatly increase the efficiency of your sanitisers, meaning that you'll be using less chemicals to sanitise your spa or hot tub water.

One of the most important chemical levels to monitor in your pool, your pH levels determines how effective your pool chlorine is and how acidic/basic your water is. To learn more about pH levels, read more here.

Pool alarms are sensors installed around the pool to inform you if something (or someone) has fallen into the pool.

These are the myriad of chemicals designed for pool use and are essential in keeping your pool sanitised and crystal clear. Mr Pool Man stocks the largest and most affordable range of pool chemicals online in Australia. If you can't find it on our online store, then it's not available anywhere online as well!

Equipment used to heat your pool, for more information, check out the Heaters entry above.

Literally the heart of your pool, your pool pump is responsible for drawing water in through your filtration system and expelling it back out into your pool. We have a detailed post on how pool pumps work here.

ECO Pumps or Variable speed pumps allow you to run your pump at lower speeds, saving you money on electricity costs and allowing you to run your pump for extended periods of time without the added burden to your bills. Read more about ECO pool pumps vs Standard pool pumps by the numbers here.

Quick drying epoxy repair material that allows you to make quick repairs to your pool system in minutes. Read more on the different uses of the Aqua Fix-it in our Mr Pool Man's Toolbox feature here.

See our entry on Chlorine Shock

A pool vacuum is used to, well, vacuum debris out from the bottom of your pool. Check out our complete guide on how to manually vacuum your pool here.

Pressure Pool Cleaners are heavy duty pool cleaners which typically use a booster pump to power it. While these were extremely popular, they're slowly being replaced by robotic pool cleaners which are more efficient and doesn't require a booster pump (or your pool pump for that matter) to power it.

The final leg in your pool filtration system, the return lines are the pipes that come after the last piece of equipment typically your salt water chlorinator.

For Mr Pool Man, Robotic pool cleaners are the best when it comes to hands-free and fuss-free pool cleaning. Robotic pool cleaners are self-contained pool cleaning robots that you simply plug in, drop in the pool and watch it go! Check out the benefits of using a robotic pool cleaner here.

A damaged rotor is usually the cause for water leaks under the handle for your sand filter multiports. Rotors work in tandem with your spider gaskets to ensure that the water in your sand filter is channeled to where it's supposed to go. For more information on multiport maintenance, we have an in-depth article which you can check out here.

Safety covers are designed to prevent things from accidentally falling into your pool. These are usually the mesh type or solid types.

Depending on your location, local regulations will require you to have safety signs like CPR signs and depth markers. If you're lookiing for pool signs that will last for years to come without fading then check out our collection of pool safety signs and depth markers here.

A salt water chlorinator takes the salt from your pool water and turns it into chlorine to sanitise your pool. There are many myths surrounding salt water pools and salt water chlorinators, we decided to debunk (and confirm) these salt water chlorinator myths in this article here. 

From its name, sanitisers are added to your pool to disinfect and clean the pool of any organic contaminants like algae and bacteria. The two most common pool sanitisers are chlorine and bromine. You can also get a salt water chlorinator or a chemical feeder to automate the sanitising of your pool for a more hands-free approach.

Scale or hard water stains usually occur near your water lines. These are caused by a high concentration of minerals in your pool or a high calcium level. Be sure to keep your calcium hardness levels in check to avoid scale.

These are usually added to pools in areas where the water has a high metal content. Sequestrants keep the metals in solution so it won't affect your waters clarity. Sequestrants do not remove metal from your pool.

Skimmer boxes serve as the first line in your pool's intake lines. These are equipped with skimmer baskets that catch any floating debris so that they won't get sucked into your intake lines and into your pool pump.

A spa is another term used for hot tubs.

Stabilised chlorine is basically your chlorine with added stabiliser / cyanuric acid. Take care and monitor your cyanuric acid levels when you use stabilised chlorine as your main pool sanitiser. Chlorine pucks or tablets are good examples of stabilised chlorine.

See our entry on Cyanuric Acid

Suction pool cleaners are the most cost-effective way of automatically cleaning your pool. If you're looking for the best value suction pool cleaners, then be sure to check out our feature on the Water TechniX Rapid Automatic Pool Cleaner.

Testing kits are something that you should always have in your arsenal. Testing kits come in a lot of forms, from ultra-convenient test strips to reagent testing kits that require more work but are more accurate than test strips. We have a comprehensive guide on how to use the different kinds of testing kits here.

Total Alkalinity is the measurement of all the alkaline substances in your pool. This is an important reading as a proper total alkalinity level will prevent wild pH swings in your pool.

The total chlorine level is the total amount of free chlorine (FC) and combined chlorine (CC) in your pool. As the rule of thumb, your free chlorine levels should always be closer to your Total Chlorine levels than your combined chlorine levels.

See our entry on pool lights and LED pool lights.

We talk about UV rays a lot especially when we're talking about pool chlorine. UV Rays can "eat up" your pool chlorine and this is where stabiliser or cyanuric acid steps in. Your stabiliser will protect your pool chlorine from the UV rays of the sun, allowing it to sanitise your pool properly. UV rays can also cause your pool equipment to crack and turn brittle, so when choosing pool equipment, be sure to pick the ones that are UV protected, like the Water TechniX line of pool cleaning equopment.

These are pool cleaners used to suck out dirt and debris from the bottom of you pool. You have the choice of manually vacuuming your pool or using automatic pool cleaners like suction pool cleaners, pressure pool cleaners, or robotic pool cleaners.

Vinyl Pools use vinyl liners, which are non-porus which makes them easier to maintain. The downside is that vinyl liners have to be replaced every few years and they are prone to damage.

To many people, winterizing is synonymous with closing the pool. Winterizing means to prepare your pool for a long period of dormancy ahead. We have a comprehensive guide on how to winterize your pool which you can check out here.

Water Harness is determined by the calcium levels in your pool. Also see our entry on calcium hardnes

Zinc Anodes or "Sacrificial anodes" are usually used in salt water pools to prevent your other pool equipment from corrosion caused by saltwater.

The sound you'll be making poolside when you rest and lounge, solid in the fact that you have a well-balance and safe pool.