Pool Info: Water Testing FAQ
What chemical levels to test for regularly?
The four main tests to perform with a test kit are pH, chlorine, Total Alkalinity and Calcium Hardness. Cyanuric Acid levels should be tested for on outdoor pools which use chlorine. Acid or Base Demand tests may also be performed with a pH test sample, to determine the amount of acid or base is needed (demanded) to make the desired change to pH level.
How often do I need to test the water?
I should say every day, 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 home pool owner should check their pH and chlorine levels 2-3x per week. If pH level has changed, check the TA level. Total Alkalinity levels tend to fluctuate less, so weekly testing is fine. Calcium Hardness and Cyanuric acid levels are slower to change, so monthly testing is recommended.
What are the recommended levels?
- pH: 7.2 - 7.8
- Chlorine: 1.0 - 2.0 ppm
- Total Alkalinity: 80 - 120 ppm
- Calcium Hardness: 200 - 400 ppm
- Cyanuric Acid: 20 - 50 ppm
- Total Dissolved Solids: below 5000 ppm
What other pool water tests can be done?
Biguanide water treatment systems use test kits, or you can use biguanide test strips to check sanitizer levels, and also the pool pH, alkalinity and calcium hardness levels.
Saltwater pools can be tested for salt with a salt test strip. if you use a salt chlorine generator, you’ll still want to test for chlorine, and you may also want to test for salt level, even if just to check it against what your controller displays.
Phosphates can be tested for with a pool phosphate test kit. Phosphates are a food for algae and can enter a pool from a variety of sources. For pools with recurring algae problems, removal of phosphates can often be a miracle cure.
Metals in the water, which can stain the surface can be tested for, with kits and strips to test copper or iron content in the water.
TDS, or total dissolved solids can be tested for with a SafeDip test meter, one that can also test for ORP, or oxidation reduction potential.
How long do test kit reagents last?
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?
Yes, you can use a pool test kit and extrapolate the bromine reading in a pool or spa. 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.
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.
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 DPD test kit will allow you to test for total chlorine levels and free chlorine levels; and the difference between the two is the combined chlorine levels. If combined chlorine is above 0.3 ppm, shock the pool to break the bond of chloramines.
When I test for pH, I get a purple color...
If your test 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 ten bucks, are usually OTO chlorine and pH testers only. You may wish to spend $10 more for a DPD chlorine kit, which measures free, combined and total chlorine levels (OTO measures only free levels).
What about pool test strips?
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. There are also strips that test hardness and cyanuric acid as well. Specialty pool test strips can test your water for minerals and metals, salt levels phosphates or bacteria.
Which pool test kit is the most accurate?
Test strips can produce different results than liquid test kits, which use especially titration tests, where the number of drops is counted and multiplied to obtain the result. Titration tests, such as those used in the Taylor K2006 FAS-DPD test kit, are the most accurate way to test pool water. Using dry tablet reagents where available, instead of liquid reagents can also improve accuracy. The LaMotte ColorQ digital test kits are also known to be very accurate pool test kits, and are used by many health inspectors.
How do I know how much chemical to add?
The best pool test kits come with booklets, with charts to use to find adjustment amounts to add to the pool, to adjust the pH, Alkalinity or Hardness, or water balance chemicals. In absence of such information, the label of the adjustment chemical should give dosage recommendations. You can also use apps on a smartphone or tablet, or sites like poolcalculator.com, to determine correct dosage amounts. It’s best not to guess at the amounts, you want to be sure. Here are some estimates for some common pool adjustment chemicals.
- pH increaser – Add 6 oz soda ash per 0.1 desired increase, per 10000 gals
- pH decreaser – Add 6 oz dry acid per 0.1 desired decrease, per 10000 gals
- Alkalinity Increaser – Add 20 oz sodium bicarb per 10 ppm desired increase, per 10000 gals
- Hardness Increaser – Add 12 oz calcium chloride per 10 ppm desired increase, per 10000 gals
- Cyanuric Acid – Add 14 oz cyanuric acid per 10 ppm desired increase, per 10000 gals
- Pool Salt – Add 8 lbs of pool salt per 100 ppm desired increase, per 10000 gals
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