Why Test your Pool Water?
Regular testing of your pool water is important for many reasons. The best of these reasons is swimmer comfort. The pH level of the eye is around 7.3 - coincidentally this is within the range of what we call "pH balanced" pool water. The skin and hair of your swimmers also prefer proper pH, as well as comfortable levels of calcium hardness. Chlorine levels are also considered part of water balance, and we know how uncomfortable it is to swim in over-chlorinated pool water.
Another reason to test your pool water is that your swimming pool also prefers balanced water. The interior pool surface can become stained or compromised when water becomes aggressive or corrosive, from low calcium or pH levels. High chlorine levels, for prolonged time periods, can damage pool liners, stain plastics and ruin rubber rings and gaskets. Improper water chemistry can also produce scale on tile and stone, and oxidize chrome handrails and underwater light rings.
Thirdly, having properly balanced water saves money. You will use less sanitizer and have fewer water problems when you balance your pH, Total Alkalinity, Calcium Hardness, Chlorine and Stabilizer levels. Your filter pump will need to run less; as you won't need to compensate for poor water chemistry with more filtration and circulation.
What Water Tests Should be Done and How Often?
Commercial pool operators keep daily logs and test the pool every few hours. For home pool purposes, testing your pool water at least weekly would be a good goal. Some chemical levels change rapidly and some more slowly over time. Cyanuric Acid (Stabilizer), Calcium Hardness and to a lesser degree, Total Alkalinity levels tend to be more stable and slower to change. pH and Chlorine levels can fluctuate in a matter of hours, with heavy sunshine, sudden rainstorms or a mass influx of swimmers.
Here's the pool water tests that should be done, and their ideal ranges to adjust to:
pH - 7.2-7.8
Total Alkalinity - 80-120 ppm (parts per million)
Calcium Hardness - 180-220 ppm
Cyanuric Acid - 30-50 ppm
Free Chlorine - 1.0-2.0 ppm
How Do I Test my Pool Water?
Water testing methods for swimming pools have become more accurate and easier to use in recent years. Smartphone apps will allow you to enter your water test readings and other information about your pool, for personalized water treatment recommendations. There are 3 main ways to test your pool water - Pool Test Strips, Water Test Kits or Digital test kits.
Pool Test Strips
The Litmus Test, also known as "pH paper", may have been the first test strip. Testing strips became very prevalent in the medical diagnosis industry during the 60's, and it wasn't long before these same manufacturers created a testing strip to check swimming pool water balance.
Pool testing strips work by dipping a 3-4 inch long strip into your pool water and swirling it back and forth for a time. The pool water will react with a number of chemical-laden comparison pads. Each one of these pads on the strip tests a different water balance parameter. The colors of the pads quickly changes, in reaction to your pool water chemistry. Compare the color of the pads to the chart on the back of the bottle. Match the color on the pad to the color on the bottle which most closely matches - each color corresponds to a different chemical level.
Pool testing strips has developed over time, and there are a wide variety of test strips now available. Modeling the product lines available with liquid, dropper-style pool test kits, test strips range from simple to sophisticated. The simple pool test strips will test for pH and Chlorine, but the more popular test strips for pools also check alkalinity, hardness and cyanuric acid levels. Test strips are also available for specialty tests like copper, phosphates or borates. And if you have a salt system on your pool, you may need salt testing strips; or for pools using a biguanide sanitizer - there's a test strip for that too.
Pool test strips are quick and easy to use, but proponents of the liquid test kits say that they aren't as accurate, due to either the technology or to frequent user error in color matching. Indeed, those who suffer from some level of color blindness will have issue with matching the colors correctly, but the same can be said for non-titration liquid test kits as well. The big advantage for test strips is that they are much easier to use and are less complicated than the liquid test kits - if that means that the water gets tested more often, then pool test strips are a valuable tool for many pool owners.
Liquid Pool Test Kits
For those that enjoyed high school chemistry, especially lab time, the liquid pool test kit may be your best choice. Liquid tests do produce a more accurate result, with easier to compare colors. There are two main types of liquid tests that can be performed, comparison and titration.
Comparison tests direct you to fill a vial with a pool water sample, then add 5 drops of the test reagent (reagents are the testing liquids used), and then compare the color in the vial to the color in the adjacent column. Tests for chlorine and pH are done in this way.
Titration tests are much more accurate than comparison tests because we don't rely on a visual color matching to determine the result. When a titration test is performed, you fill a vial with a pool water sample, then add an indicator solution. Swirl to mix. Then, add the titrant - dropwise (or drop by drop), and count the number of drops it takes to make a complete color change. Then refer to a chart with gallons on the vertical axis and desired adjustment on the horizontal - and you can find how much chemical you need to add to the pool. Tests for Total Alkalinity, Calcium Hardness are done with titration type testing.
Turbidity tests are used when testing for Cyanuric Acid in your water. Usually called Stabilizer or Conditioner, Cyanuric Acid helps extend your chlorine by shielding it from most of the effects of UV radiation. A turbidity test is rather interesting. It uses a melamine reagent which reacts with the cyanuric and causes it to precipitate out of solution. This makes the water cloudy, or turbid. After the reagent is added to a vial containing a pool water sample, it is mixed for 20 seconds. Pour this solution into the vial containing a black dot in the bottom, and stop filling when the dot becomes invisible due to the cloudy water. Read the cyanuric acid level printed on side of the tube, at the level of the water.
Residential water test kits typically contain a standard visual comparator test tube, Taylor Test Kits model shown on the left. Commercial pool operators may be required to use more accurate and precise measurements to meet health department standards. The slide comparator, used by many pool professionals, has glass panels which won't fade and many more of them to make better comparisons of slight color differences.
DPD vs. OTO
There are two types of test reagents that can be used when testing for chlorine. OTO (short for Orthotolidine) turns yellow in the presence of chlorine. DPD turns pink in the presence of chlorine. But DPD takes chlorine measurement to another level, by measuring not just Free Available Chlorine (FAC), but by adding another reagent, you can discern the level of Total Available Chlorine. The difference between the two, if any determines the presence and level of Combined Chlorine, or Chloramines. DPD testing lets you know when to shock the pool to remove these foul smelling, ineffective sanitizers - chloramines.
DPD vs. FAS-DPD
Commercial pool operators may also be required to use the DPD-FAS method of testing for Free Available Chlorine. This is simply a DPD test that uses a titration test, instead of the less accurate comparison test. Instead of going from clear to pink, FAS test kits go from pink to clear. After adding a DPD powder, the sample will turn pink (if chlorine is present). Then add Ferrous Ammonium Sulfate (FAS), drop by drop, until the color changes to clear. Refer to the chart for the most accurate measurement of free chlorine.
Digital Pool Water Testers
A new breed of testing has come of age in recent years. It started with simple meters that could test only one thing, pH or TDS (Total Dissolved Solids), but have matured to more fully featured and self contained units that can even interface with online personal databases. There are 4 main types of digital pool water testing equipment.
Digital Meters: These are electronic, battery operated and hand-held devices that use metallic probes and powerful internal software to measure various, but usually not all chemical parameters. It's common to find digital meters for pH, chlorine or TDS, but not one that will also measure Total Alkalinity, Calcium Hardness or Cyanuric Acid.
Digital meters are good at measuring salts and pH in the water, and as an added bonus, can check your water temperature. They can be very useful for the pool owner using a salt chlorine system, and because they can measure ORP (Oxidation Reduction Potential), it helps commercial pool operators meet this requirement, and allows them to keep these levels proper.
The best digital testing meter that I have seen lately is the Safe Dip Digital Pool & Spa Chemistry tester. Measures pH, FC (free chlorine), Salt, TDS, ORP, Temperature. It won't check your Alkalinity or Calcium Hardness levels, but these levels do not change very fast or often, so a separate test every few months would be sufficient.
Photometric Scanners: Favorite of my local health department inspector, test kits like those offered by ColorQ . They use an internal Spectro-photometer, and powerful, onboard software to calculate precise readings. Users insert a vial with a pool water sample and a liquid or tablet reagent, and the hand-held scanner takes over. Will test your pool for a wide variety of water balance parameters, while removing environmental factors which can skew your test results. This type of digital pool water tester also computes the recommended amounts of chemical to add to your pool, if an adjustment is necessary.
Digital Strip Readers: AquaChek is a leading brand of pool testing strips. They created a photometric reader that will make consistently precise readings from the comparison pads on specialized test strips made to work with their digital strip reader. It tests for Chlorine, pH and Alkalinity and will store the previous 9 tests so that you can spot any trends with your water balance. Just dip your strip, and insert it into the digital strip reader.
Water Testing Apps: There are many apps available now for smartphones and tablets, using the Apple or Android operating system. The most basic apps will give back water balance adjustment recommendations when you enter in your test results. Other apps will actually read the test strip by taking a photo of it and matching the comparison pads of your strip to its database of colors. Special test strips are required to use some strip reader apps, however some support a wider variety of popular test strips.
I hope you enjoyed this blog post on water testing kits, and how to test your pool water. Remember to test your water at least weekly; your swimmers and your pool will be more comfortable!
SPP Pool Enthusiast