Yes, There's a wrong way to test your pool water

If you haven’t checked out our Ultimate Guide to Testing your pool water, then don’t forget to check it out after going through this blog post. Today we’re going to go over the ways of how we can incorrectly test our pool water. Yes, there are actually ways that you can incorrectly test your water!

Getting a sample from the wrong area of the pool

You might be saying, but it’s all the same water! While that may be true to some extent, different parts of your pool will give you different readings, and what we want is to get the most “true” readings so we can properly add the right amount of pool chemicals to balance your pool. Here are the locations where you shouldn’t get your testing samples from:

  • Near the surface - The chemistry of the pool water near the water will be somewhat different than the rest of the pool. Surface water is warmer, it has more contaminants like floating body oils, debris, floating bugs, and other things that may skew the test readings.
  • Near return jets / intake lines - These two locations will also have “off” chemical readings as well. Water coming from the return jets is freshly filtered and if you have a salt water chlorinator, you’ll get better chlorine readings that what is representative of your pool. If you get water from near the intake lines or your skimmer, you’ll also get skewed readings.
  • Near Corners / Steps / Ladders - These locations don’t get as much circulation as the rest of your pool so avoid getting water samples from these locations as much as possible or how much you’re tempted to get your samples from these locations because of ease of access.

Where’s the sweet spot for getting your water sample? Somewhere away from the locations mentioned previously and water at least a foot down (or until your elbow) in depth!

Not testing the sample immediately

As much as possible, test the sample that you’ve retrieved immediately. Don’t set it down somewhere and get back to it. Once you start the testing process, follow through and test immediately. Why? Once the water is out of the pool, it starts to interact with the air, evaporate, increase temperature, and other things that may affect your readings. Remember we wanted to get the sample from the proper location, so don’t waste the effort and leave the sample in the open to degrade.

SEE: How To Treat Pool Water For The First Time

Having too much or too little water

This is only applicable to reagent test kits. The testing vials have recommended water levels and they’re there for a reason. The reagent reactions are actually calibrated by volume and any change in the volume of water being tested will affect the test results as well.

Having too much or too little reagents

Believe it or not, there is actually a wrong way to use the reagent dropper. The right way to use it is to hold the reagent bottle vertically to get the proper drop sizes for your reagents. Tilting the reagent bottle at an angle will allow air to slip through and can possibly create smaller or larger reagent drops than what is normally produced when holding the bottle vertically. If you’re using tablet-type reagents, use the entire tablet and don’t skimp on the reagents! Using half a tablet will only give you half the reaction and will give you an incorrect reading.

Having bad reagents

There are many reasons why you may have bad reagents and simply put, having bad reagents can give you bad results! Here are some reasons why you may have bad reagents.

  • Expired Reagents - This is one of the reasons why you shouldn’t skimp on testing and reagent use. Pool testing reagents usually have an expiration date of two years from the date of production, but some may have a shorter lifespan than that, be sure to check the bottles for their expiration dates. One thing to note, once reagents are opened, another timer will start to tick down and they may go bad even before the printed expiration date because of their exposure to air. So just keep on testing!
  • Improperly stored reagents - Pool testing reagents should be stored in a cool place away from direct sunlight because UV rays and temperature will greatly affect the efficacy of your test reagents.
  • Cracked or damaged reagent bottles - If you spot damage on your reagent bottles then there’s large chance that the reagents inside are compromised and will not give you accurate results. Replace as needed.

Mixing Reagents

While some people will say that a test reagent is a test reagent no matter who produces it, it’s still worth noting that it’s never a good idea to use different reagents from different manufacturers. This isn’t about brand loyalty (although there’s nothing wrong about that) but simply because different manufacturers will have different calibrations for their testing kits. How can they be different? Well, the volume of water per test is one, reagent bottle dropper size is another, different color schemes is another, and a slew of other manufacturer specifications that may not seem apparent at first.

Contaminated Reagents

By design, pool testing reagents react with other chemicals, so once they’re contaminated with something else they’re basically “used up” and will no longer be accurate. The main cause for contaminated reagents is mixing up reagent caps (some bits of reagents may be left of the covers) and leaving reagents uncovered for extended periods of time. So after using a reagent bottle, return the caps immediately to avoid contaminating your reagents.

Contamination doesn’t only come from the source, but it can be at the testing vessels as well! Dried up reagents from previous tests will definitely skew your test results! So after a testing session, rinse out your test vessels thoroughly and allow them to dry or let them stand upside-down to ensure that no water droplets remain.

Faded Color Charts and Test Vessels

This goes without saying, if your color charts are faded then it’s time to get a new kit. Remember, to properly determine your pool chemical levels, you’re visually comparing the results with the calibrated color chart. If the charts are discolored then the results are off! Another thing that may be throwing off your test results is if your test vessels start to get scratched and they start to turn opaque. The light passing through the vessel will be affected which will lead to a wrong interpretation of the results.


Testing your pool water is one of the most important aspects of pool ownership and this is why it’s very important to ensure that pool testing is done properly as not to waste time and to make sure that your pool is completely safe! If you're having any of the issues mentioned above with your testing kit, get a new one and don't delay! Remember, your test results are only as good as your testing kit and technique.
Check out our Mr Pool Man’s Toolbox – Pool Tools & Supplies here.


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Happy swimming :)

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