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Water Testing

Keep your pool water clean and balanced so it will last a lifetime. Let our professional staff here at Prime Time pool take the worry and drudgery out of keeping your pool clear and safe all summer long.

The subject of water testing may transport you back to the days when you were in school and final exams were approaching all too quickly for your comfort. Rest assured, pool water tests are much less painful than you may imagine. What's more, regularly testing your pool water is a critical part of any maintenance routine. Each element defined in the Keeping Your Water Balanced section has a specific test to give you an up-to-the-minute evaluation of your pool water. Once again, your pool supply shop is the best place to buy these test kits. To give you a brief outline of their use, we review all the various tests you or your service professional must perform on your pool.

Sanitizer/oxidizer tests

Measuring Sanitizer and Oxidizer levels

There are two well-known test kits available to test levels of chlorine and bromine, the DPD and OTO. Each has a long, scientific nam, but all you really need to know are the initials. The DPD is the preferred of the two because it tests for free available chlorine the most powerful "killing form" of chlorine. Its chemical reagent reacts with the free available chlorine in the sample water to change its color. The ideal range of 1.0 to 3.0 ppm for pools will command a pink to red color. To get an accurate reading, just compare your test sample to the manufacturer's chart that should be included with the test kit. Note: An extremely high level of chlorine tends to bleach out the test water, making it appear as if there isn't any chlorine present. This would normally prompt you to add more chlorine, and in most cases, that's correct. If you think you have received a false reading, conduct the test again, except this time, fill the test vial with 50 percent chlorine-free or tap water and multiply the results by two. This will help you determine whether you have a low level or very high level of chlorine in your water. The other, less common, test is the OTO, which works on the same basic principle, but will turn the water yellow to deep orange when chlorine is in the proper range. One of the major differences between the OTO test and the DPD test is that OTO cannot distinguish between total chlorine and free available chlorine. You won't get an accurate estimate of how much killing chlorine is in your pool water. A final note: Bromine can also be tested using either method, but the results need to be multiplied by 2.25 to yield a true reading - - unless, of course, you have one of the test kits that include a bromine color chart as a reference. So far so good? Let's move on to pH.

PH Readings

Protecting your guests and pool equipment

The most common pH test for pool owners is the phenol-red test. Just like the DPD and the OTO, the phenol-red test has a reagent that mixes with the acid in the water to cause a color change in the sample. If your pH is in the correct range, the water sample should turn a shade of red ranging from pink to orange. If you get a yellow result, you have a low pH or acidic water. If the color is a deep purple, your pH is too high. Once again, you'll need to compare your results with the color chart provided with the test kit to get an accurate reading. Adjusting pH is a very simple task. If you have a low pH, add soda ash or sodium bicarbonate. If your water's pH is high, add liquid muriatic acid or dry acid. Before you attempt to change the pH, however, you need to perform a second test to figure out how much of which substance you'll need to add to the water. A base-demand test determines how much soda ash or bicarb is required and an acid-demand test calculates how much muriatic or dry acid is needed. These tests are called titration tests or end-point reactions. In this type, the number of drops of a special liquid it takes to cause a color change corresponds with the amount of soda ash or acid required. Consult the test kit manufacturer's recommendations for the exact amounts. One more caution: Before doing anything about your pH levels, you also need to test the total alkalinity of your pool water, as described below.

Testing Your Water

Tesing your pool water is a must.

The subject of water testing may transport you back to the days when you were in school and final exams were approaching all too quickly for your comfort...

Total alkalinity test

Tesing your pool water is a must.

This test the last of the regularly performed tests measures total alkalinity. As noted above, this test should be done before you do your pH test and adjustments. The two factors are interrelated and must be dealt with together. Total alkalinity is determined by using a titration test with two reagents. The first changes the color of the test sample, the second triggers an end-point reaction. It's with the second test you count the number of drops of reagent added to the pool water sample, swirling the sample after each drop until it changes color. Note: This reaction occurs very suddenly so don't add the second reagent too quickly.

Calcium hardness levels

Tesing your pool water is a must.

Tests for calcium hardness are performed at the beginning of the swim season, when you start up a new pool or after draining and refilling a pool. After that, they only need to be done every three months or so. But don't forget about it entirely because when allowed to go too high or too low, the water's hardness levels can cause all kinds of problems. (For more on water hardness, see the section on Keeping Your Water Balanced.) Like total alkalinity, an end-point reaction best measures calcium hardness. The first reagent is a pH buffer to bring the pH level up to approximately 10. The second step adds a dye that, when reacting with calcium, turns the sample water a different color. Next, the titrant (EDTA) is added one drop at a time until the water changes color. The total number of drops required gives you the amount of hardness when compared with a manufacturer's chart.


Give your chlorine levels a quick boot.

Every once in a while, your pool water may become a veritable hotel of unwelcome contaminants and bather waste products. You can often detect when this happens because a "chlorine" odor may begin emanating from your pool, or you may notice that you're experiencing some skin and eye irritation. But the most reliable and better way to monitor your water quality is to take a second look at your sanitizer readings. If your chlorine test readings keep dropping hard and fast, you may be faced with the need to evict chloramines from the water. (For more on how chloramines form, see the section on Keeping Your Water Balanced.) This is done easily enough with a process called shocking. No, you don't electrocute the chloramines. What this process entails is adding extra high doses of sanitizers to the water. By adding a large dose of chlorine a process called superchlorination or shocking you bring up your residual of free available sanitizer in a relatively short period of time. The newly added sanitizer will promptly rid your pool water of those annoying guests. To be safe, do not use your pool for at least 24 hours after shocking with chlorine. You should also test for the proper sanitizer levels before getting back in the water. Note: There are non chlorine shocking products available that lessen the amount of time swimmers need to stay out of the pool. Check with your local pool supply store or professional service technician for more information.


Because time and contaminants wait for no man.

So, how often do you need to conduct these tests? It depends on the time of year, your geographical area and how often you use your pool. For example, a pool owner in Vermont who swims laps twice a week wouldn't need to test his water as often as an owner in Arizona where there's a higher rate of evaporation, more direct sunlight eating up the chlorine and, say, a regular stream of neighborhood kids coming over for a little water fun. You get the point. There are, however, some basic testing guidelines you can follow.


Manage your sanitizer levels

You should test for your chlorine or bromine levels three or four times a week if you're using your pool regularly and once every week or two if you're not. Remember, your goal is to maintain at least the minimum amount of sanitizer residual at all times. Depending on how often you use your pool and other factors such as geography you may need to test more often. It's also very important to test the water after a rainfall which can dramatically impact your water balance.


This should also be tested often during heavy use of your pool at least three or four times a week if not more. In fact, these tests should be done in conjunction with sanitizer testing. One convenient way to remember is to always test one if you test the other.

Total Alkalinity

You should test your pool water often during heavy use perhaps once a week and as called for if there are any dramatic changes in your pH levels.

Calcium Hardness

Test the pool water and the tap water you add whenever you first start up your pool. You should then follow up with more tests every three months or if you see any scale formation.


For the best test results, you should also keep the following points in mind as you set up a testing routine.

  • Test-kit reagents can deteriorate over time and will eventually give you false results. Always check the expiration dates and follow the manufacturer's instructions for usage and storage.
  • It's very important to clean your test kit after each use. Any residual chemicals can hamper your efforts at finding and maintaining the right water balance.
  • Only test pool water that has been circulating for a while and always get your sample from at least 12 inches below the surface.
  • Read your results immediately using a brightly lighted background, preferably white.
  • Do not use your fingers in place of a test vial cap because the oils from your skin can skew your results.
  • Finally, and most importantly, always record your results. A running history will keep you informed and give you vital information if you start having any trouble with the water in your pool.


In reading all this information about water chemistry and testing, don't become discouraged. It may sound confusing at first but taking care of a pool is a simple, routine task. Once you know what to look for and how to properly test your water, you'll be more than able to keep your backyard oasis just that a relaxing, stress-free getaway.

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