The beginning of warm weather means the beginning of pool season. That's when it's time to begin checking your water quality. In a typical residential swimming pool, this means that you need to routinely check for:
- Total alkalinity
- Acid demand
And there are other tests you may need to do, as well. This might sound complicated, but don't worry if you didn't ace chemistry in school—pool test kits are fairly easy to use if you follow the directions.
Standard test kits will accurately test for the four or five principal tests most homeowners need. There are also specialty tests that can be conducted in certain circumstances:
- Biguanide water treatment systems, found on some swimming pools, require biguanide test strips to check the sanitizer levels, pool pH, alkalinity, and calcium hardness levels.
- Test for salt on saltwater pools using a salt test strip. if you use a salt-chlorine generator, you will also need to test for chlorine.
- Phosphates can be tested using a phosphate test kit. Phosphate can enter a pool from a variety of sources, such as lawn fertilizers, and they can lead to algae that feed on the phosphates.
- If pool water stains the surface of your pool, you can test for metals such as copper or iron using special test strips designed for the purpose.
- Chloramines (combined chlorine) can be tested with a DPD test kit. ShockCheck test strips can tell you when shocking is needed to remove chloramine.
- TDS (total dissolved solids) can be tested with a SafeDip test meter.
Discoloration on the walls of a pool often indicates the presence of algae, which requires more frequent testing and super-chlorinating (shocking) the pool.
Working With Test Kits
Standard kits for testing water chemistry come in several different types. The particular kit used in this demonstration, the 4-in-1 by Biolab Guardex, tests your pool water's pH, chlorine, acid demand, and total alkalinity. Other available kits are 2-in-1 (chlorine and pH); 5-in-1 (chlorine, bromine, alkalinity, pH, and acid demand); or 6-in-1 (chlorine, bromine, pH, total alkalinity, total hardness, and cyanuric acid).
Other types of kits include test strips or provide analysis through the manufacturer's website or an app or online calculator. You can also get a reading by taking the kit to your pool supply store. Be aware that the bottle numbers, vial sizes, and chemicals in this project are unique to this particular brand of test kit. Follow the instructions for your kit; usually, you can find them online.
When to Test Pool Water
There is no set guideline for when to conduct various tests on pool water chemistry. Some people test all components daily, and this is a perfectly acceptable, if slightly obsessive, schedule. However, many pool experts suggest the following schedule for testing:
- Chlorine levels: two or three times each week
- pH: two or three times each week
- Acid demand test: whenever pH levels need adjustment
- Total alkalinity: weekly, unless pH has changed, in which case you should always test the total alkalinity (TA)
- Calcium hardness: monthly
- Cyanuric acid levels: monthly
- Total dissolved solids (TDS): monthly
Equipment / Tools
- Four-way pool water test kit
Take a Water Sample
Dip the plastic tester into your pool, making sure you draw water from a depth of at least 18 inches for an accurate "catch." Water chemistry near the surface of the pool may not be typical of the water deeper in the pool.
Check the Vial Levels
Make sure the vials are filled to the marked "fill" line on the column. Proper readings require a precise ratio of pool water to the testing solution.
Test for Free Chlorine and Residual Chlorine
Add five drops of solution No. 1 to the column for testing chlorine. In this kit, the chlorine indicator solution happens to be ortho-Tolidin.
Note: Some test kits use dissolving tablets rather than a liquid testing solution.
Mix the Solution
Place the caps on vials and invert or turn the vials upside down several times to mix the solution with the pool water.
Compare the Colors
Wait a few seconds, then compare the color in the vial with the color standards indicated on the plastic tester. This will give you a reading of the free chlorine level.
Wait a couple of minutes and compare the colors again to determine the residual chlorine level.
Note: Some kits have two separate tests for free chlorine and residual chlorine, each requiring different solutions or tablets.
Test the Pool's pH Levels
After rising the tester clean, fill the large tube to the top solid line with pool water taken from a depth of 18 inches. Add one drop of solution No. 4 and mix it by gently swirling the tube. This solution is sodium thiosulfate, a chlorine neutralizer. Add five drops of Solution 2, a phenol red indicator, and mix by gently swirling. Compare the color with the pH color standards on the plastic tester to determine the pH level of your pool water.
Note: Don’t perform this test if the residual chlorine is above 3.0, as you will not get an accurate pH reading. The residual chlorine must first be adjusted to normal levels.
Test for Acid Demand
Using a sample of the water from the pH test, add the acid demand titrant. Count each drop—making sure to swirl between drops—until the color matches that of the 7.4 indicator. Refer to the acid dosage chart to determine the correct amount of acid to add to your pool to balance the pH.
Note: Don’t perform this test if the pH is above 7.5 and the chlorine residual is above 3.0. The residual chlorine must first be brought to proper levels before testing for acid demand.
Test for Total Alkalinity
After rinsing the tester clean, fill the large tube to the lower dash line. Add one drop of No. 4 solution and swirl. Next, add one drop of solution No. 5B, a total alkalinity indicator, and swirl. Add No. 3 solution, drop by drop (make sure to keep track) until the color changes to clear, light yellow, or light green.
Finally, multiply the number of drops of solution No. 3 you used by 10 to determine the total alkalinity.
Note: Don't perform this test if the residual chlorine is above 3.0. Chlorine must be in normal ranges before testing for TA (total alkalinity).
Rinse and Dry the Tester
After testing, rinse your plastic tester in a sink (never in the pool), then dry it completely. Pack up the kit and store it in a cool, dry place, away from children.
Tips for Testing Pool Water
- Don’t buy more pool chemicals than you’ll use in a season, because they can lose effectiveness over time. The test solutions (reagents) typically last about one year.
- Avoid test strips. Test strips are available to conduct individual tests simply by dipping the strips into the pool water and "reading" the color. However, these are not as accurate as test kits that mix the water with a reacting solution.
- When you run out of testing solutions, you can purchase replenishment bottles rather than buying an entire testing kit.
- Comprehensive kits are available that offer the testing solutions and materials required for nearly any chemical test you might need. These deluxe kits can cost between $30 and $60.