How to Test Your Pool Water

You take pride in your swimming pool for a good reason. Now you’re ready to open it for the season and want to keep your pool safe, sanitary, and crystal clear. Pool water testing is the best thing you can do to ensure safe and clean water.

First, let’s cover why testing is so important and what kinds of tests you should do. After that, I’ll dive into how to test for all the chemical readings you need.

Why Testing Your Pool Water Is Important

While it looks like a pond, your pool is more of a chemistry lab. The chemicals in your pool can either keep it clean or make it potentially dangerous. Testing your water is the only way to know for sure what those invisible chemicals are doing in your water.

You need to test your water often. While it might seem like a hassle, it’s a good thing! The better balanced your water is, the less cleaning and water changing you have to do.

When and How Often to Test Your Pool

You can test pool water yourself, but if you don’t feel super comfortable doing that, you can also take a sample for professional testing when you open and close your pool. Most local pool supply stores like Leslie’s can test your water for you. The second set of eyes keeps it safe and clean. On the whole, you should be testing your swimming pool at least once a month in addition to when you open and close it for the season.

Regular testing is essential for your chlorine, alkalinity, and pH levels. It’s so significant that the CDC calls chlorine and pH your “disinfecting team.” The minimum testing schedule for pH and chlorine is weekly, starting before you open your pool.

There are other times that you should test for balanced levels, though, including:

  • After a rainstorm
  • After large groups have used the pool
  • Before beginning any form of algae treatment (pH testing is mandatory here)
  • After changes in the weather
  • After adding water
  • Before you close your pool
  • If you notice any issues with your water, like cloudiness or color changes

Some other necessary testing you need to do to maintain excellent pool water is for cyanuric acid (CYA) and calcium hardness. You also test for copper, iron, and calcium. We’ll also cover testing for phosphates and salt. We’ll give a schedule for these tests in the instructions below.

Step-by-Step Process for Accurately Testing Your Pool Water

Each section below will cover the basics and walk through steps you can follow. I’ll also cover how to sample your water correctly and use your testing equipment.

Gathering a Proper Water Sample

Take samples far from your skimmer and return jets and well below the surface (try for the middle). Use a clean container test container. If you bring the sample to a store, make sure it has a lid.

  1. Hold the container in your hand, like in the picture above, outside of the water. Now, turn the opening down towards the bottom of the pool.
  2. Push the collection container into the water, well below the surface. Keep it facing the bottom. You want air trapped inside of it at this point.
  3. Turn your hand below the surface, so the air escapes and looks like the picture above.

How to Use Water Testing Kits

There are three main kinds of test kits:

  • Liquid Testing Kits
  • Testing Strips
  • Digital Testing Kits

How to Use Liquid Testing Kits

Liquid testing kits cover most homeowners’ basic needs for testing regularly. They are accurate when used correctly. However, they are also finicky and can give you inaccurate results due to user error.

For testing pH, your kit needs to have two things: Orthotolidine (OTO) to test chlorine and phenol red. Keep a sheet of plain white paper in your test kit.

After taking your sample according to the instructions above:

  1. Add the correct number of drops of OTO to the chlorine side
  2. Add the correct number of drops of phenol red to the pH side
  3. Place your white paper behind the test kit, so you can clearly see the color results
    1. The redder the pH side, the higher the pH
    2. The yellower the chlorine side, the higher the chlorine.
  4. Compare colors to any chart given with your test kit to determine levels

How to Use Testing Strips

You use less liquid testing materials than you use test strips. However, the accuracy of the strips can’t be denied, and they often have all the things you need to test in one strip. They are also much easier to use. You’ll go through more, but they’re also cheaper.

Testing strips do the basics, alkalinity, pH, and chlorine. There are test strips for copper, iron, bromine, and salt, as well.

After taking your sample, as explained above:

  1. Take one test strip from the container, dip it into the water, and remove it.
  2. Hold your test strip level test dots up or place it on a level surface for the time recommended (Do not shake it. It’s not a polaroid.).
  3. Match up the colors on the strip to the colors on the packaging.

How to Use Digital Testing Kits

Digital testing kits are pretty simple to use. Using these liquid test kits minimizes user error because the digital screen displays your exact results. These tests can read free chlorine and total chlorine, CYA, alkalinity, pH, calcium hardness, and bromine (Not sure what that is? Read my guide on chlorine vs. bromine).

Each digital test kit is a little different, but you’ll want to gather a sample as explained above and follow the instructions for your unit.

There are also apps, but these are calculators and scheduling tools, not testers.

Testing for the Basics: Ph, Alkalinity, Chlorine, Cyanuric Acid, and Calcium Hardness

Testing for chlorine, pH, and alkalinity are very similar actions. Here, we’ll cover how to test for everything you should.

Testing for Alkalinity

Alkalinity testing measures buffers, your pool’s ability to maintain a steady pH level. If it’s too high, it’s really hard to change pH; if it’s too low, pH will change very often. People can change the pH simply by going into the water if there’s no buffer.

Testing alkalinity first is the best practice, as it affects your ability to change pH. However, if your pH is below 7.0, you want to raise it first and then test alkalinity again.

If you use test strips, then the chances are that they test for this. Follow the instructions for how to use the test strips above. If you purchase a liquid testing kit, it’s more complex.

After taking the water sample, as explained above, you will use three testing liquids at different times.

  1. Read your test’s instructions, know how many drops of the first two test liquids, and how much water you need.
  2. Add first test liquid drops to the water, Sodium Thiosulfate, and swirl to mix.
  3. Add the second, the total alkalinity test liquid, and swirl to mix until the color is green.
  4. Add drops of the sulphuric acid one at a time, counting and circling each in until the color changes to red.
  5. Take the number of sulphuric acid drops and multiply by 10 to tell you the total alkalinity. Eight drops mean an 80 total alkalinity (measured in ppm), which is low, and ten drops (100) is on the higher end of the acceptable range.
  6. Take action to raise or lower your alkalinity if needed.

Use my alkalinity calculator to help you get in the ideal range.

Testing for pH, Cyanuric Acid, Calcium Hardness, and Chlorine

We’ve already discussed the importance of testing for chlorine and pH. Calcium hardness is also known as water hardness. Hard water can leave deposits on your pool, in your filter, and in the plumbing.

Cyanuric acid is a protectant; it keeps your sanitizer safe from the sun’s UV rays. However, too much of it can cause your chlorine itself to work so slowly that it can’t sanitize your pool. Conversely, too much chlorine in your pool can pose some fabric fading and health risks. Use my pool chlorine calculator and stabilizer calculator to help you get your sanitizer in the correct range.

If your pH levels are too low (the ideal range is 7.2-7.4), make sure to take the proper steps to raise your pH level to the right range. You can use my pH calculator for that.

Depending on the type of testing media, either strips or liquids, follow the directions outlined above for using your test kit.

Testing for Copper

Copper and iron are both metals; they come into your pool in many ways. However, low acid levels are associated with rising levels of metals in your pool. Most test strips for pools don’t test for copper or iron, but test strips that do generally test for both.

Follow the directions above for strips or a liquid test kit.

Schedule for Testing Pool Water for Copper

Once a month. If you have a low pH test, you may want to test at that time, also.

Testing for Iron

If you get too much iron in your water, your pool will turn brown with rust stains. Low pH levels can accompany iron being introduced into your pool. As stated above, you’ll need special strips for this and a special liquid. However, the testing is much the same as your weekly tests.

Schedule for Testing Pool Water for Iron

Once a month. You should test if you notice a brown coloration or have a low pH reading.

Testing for Calcium

This is the same as testing for calcium hardness or water hardness.

Schedule for Testing Pool Water for Calcium

Once a month.

Testing for Phosphates

This one is simple, you can test for phosphates, but you don’t ever need to. Phosphates, while they are food for algae, are naturally occurring, so lowering them won’t help you avoid an algae bloom.

Schedule for Testing Pool Water for Phosphates

None, it’s not necessary, but you can do it if you want to.

Testing for Salt

You only test for salt if you have a saltwater pool. Too much salt can cause your salt chlorination to go crazy, producing too much chlorine. Too little, and it won’t make enough to sanitize your pool. Salt test kits come in liquid and strips, also. If you have a saltwater pool that is turning green, you likely have an algae problem.

Schedule for Testing Pool Water for Salt

You should test your salt levels monthly. However, if you add water, have a rainstorm, or have heavy use, those are all reasons to test immediately. For more, read my complete guide on how to test the salt level in your pool.

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Ready to Test?

There you have it! Questions? Shoot me a message, and I’ll be happy to help.

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