Pool Info: Water Testing FAQ
Water Testing FAQ
What chemical levels do I need to test for regularly?
The four main tests to perform with a test kit are pH, chlorine (or other sanitizer residual), Total Alkalinity and Calcium Hardness. Cyanuric Acid levels should be maintained on outdoor pools which use chlorine. Mineral content, Total Dissolved Solids and Acid or Base Demand tests may also be performed as needed.
How often do I need to test the water?
I should say everyday, but I realize that's a bit much for most people. Commercial pools are required to check chlorine levels every hour and record their findings in a log, however the "backyard lifeguards" should check their pH and chlorine levels at least twice per week. Chlorine should be fed continuously through a feeder device to maintain a consistent level. Total Alkalinity and Calcium Hardness levels tend to fluctuate less, so weekly testing should be O.K.
What are the recommended levels?
pH: 7.2 - 7.8
Chlorine: 1.0 - 2.0 ppm
Total Alkalinity: 80 - 120 ppm
Calcium Hardness: 180 - 220 ppm, though some say 200 - 400.
Cyanuric Acid: 40 - 80 ppm
Total Dissolved Solids: below 5000 ppm
How long do my reagents last?
Typically one season. Reagents lose their strength over time and can also be ruined by direct sunlight and temperature extremes. Replace your reagents annually. Reagents (or test strips) that give suspect readings should be looked at suspicously.
Can I use reagents from other test kits with my test kit?
No; drop size, concentration and color variation will provide inaccurate results. Only use the reagents made by the manufacturer of your test kit. Same with certain digital strip readers or even smartphone apps that read strips are most accurate measuring their own strips.
Can I use a chlorine test kit for bromine?
If you have a DPD test kit, you need simply multiply the test result by 2.25 to obtain the bromine equivalency. This works because bromine is over twice as dense as chlorine. Yes, you can use a dpd test kit and extrapolate the bromine reading in a pool or spa.
My test kit shows no Chlorine, even though I know it's there...
If chlorine levels are excessively high, the content can bleach out DPD, a reagent commonly used for chlorine testing. Either dilute the sample with chlorine free water, or double the # of drops of DPD, and multiply or divide accordingly.
There has been evidence that excessively high levels of stabilizer, or cyanuric acid, can cause a phenomenon called chlorine lock. Levels above 100ppm of cyanuric acid (CYA) may prevent chlorine from registering and possibly sanitizing. Lower CYA levels by dilution.
If you smell chlorine in the water, you are very possibly aware of combined chlorine, known as chloramines. These will not register in a test for free chlorine. A good DPD test kit will allow you to test for total chlorine levels and free chlorine levels; the difference being the combined levels. If trace amounts of combined chlorine is above .3 ppm, you may need to shock the pool to break the bond of chloramines; this shock level is around 30 ppm.
When I test for pH, I get a purple color...
If your reagents are in good condition, a purple color in a pH test is an indication of chlorine levels being too high and interfering with the test. Add a drop of thiosulfate reagent (#7 in the Taylor test kit) to remove the chlorine from a new sample, and test again.
What type of test kit do I need?
There are many different types of test kits commercially available. If you are concerned about water balance, (and you should be) you will want to spend more for a nice kit. The basic "duo" test kits, available for about five bucks, are usually OTO chlorine and pH testers only. You may wish to spend more for a DPD chlorine kit, which measures free, combined and total chlorine levels (OTO measures only free levels). Also important is the ability to test total alkalinity and calcium hardness. Acid demand and base demand tests will allow you to perform a titration test on your pH sample. Simply count the # of drops to determine, with the help of a chart, exactly how much acid or base is needed to adjust the pH. A "four-way" test kit will test pH, chlorine, alkalinity and acid demand.
Test strips are available with "Litmus test" technology. These are "dip & read" strips of paper that turn colors indicating levels of pH, alkalinity and chlorine in the pool. Fairly simple to use, however, it seems that they may not be quite as accurate. Modern devices will improve accuracy and help those who cannot discren the colors very well. Your pool professional can check the water for metal presence, cyanuric acid levels and TDS (total dissolved solids).
If you have a biguanide water treatment system or a chlorine generator, you'll obtain special test kits from these dealers.