Test Kits for Treating Your Pool Water
By Debra Maurer
Think it’s a bad sign if your swimming pool water changes colors? Sure, if it turns an unsightly green, you’ve got a problem on your hands. But sometimes it takes a little color-changing to keep the entire swimming pool crystal clear. To check the chemical levels in your water, many test kits rely on a vial of water turning a shade of pink, while others make several different colors appear on a test strip. Some don’t rely on color at all and instead give you a digital reading of important parameters, such as sanitizer, pH, and alkalinity. Whatever method you choose, you want to be sure the results are clear and accurate to keep your swimming pool water sparkling.
Types of Test Kits
Test strips have gained popularity in the past decade and are used by the majority of swimming pool owners. Though often not as precise as wet chemistry kits, some owners find them more convenient because there’s no need to add chemical reagents (substances that react with dissolved chemicals and elements to change the water’s color), as the strips already contain them. Users dip or swirl one of the strips in the water, wait the prescribed amount of time, then compare the colors appearing on the strip to the color comparator on the bottle. For accurate results, it’s critical to follow the product’s precise instructions. A bottle of 50 strips that test for multiple parameters (chlorine, bromine, pH, and so on) costs $7 to $16. Strips that measure specific substances, such as iron or copper, typically come in packs of 10 or 25 and range from $14 to $22.
Digital test strip readers take the subjectivity out of reading results. A basic reader for consumers hit the market about two years ago and has gradually gained market share due to its ease of use. Users simply place a test strip in the reader, and the reader’s LCD screen will display free chlorine, pH, and alkalinity levels. The digital reader retails for $50, and a bottle of replacement strips is about $11.
Wet chemistry kits allow swimming pool owners to do more specific testing. They provide a color comparator block attached to a plastic vial, which you fill with pool water. Though some chemical reagents come in powder form, you will generally add a few drops of liquid reagents to the water sample and compare the water’s color to the comparator block. Wet chemistry kits come in two main forms: OTO (orthotolidine) and DPD (diethyl-p- phenylenediamine). FAS-DPD (ferrous ammonium sulfate-DPD) is a more advanced type of DPD, used primarily by professionals, in which users add a certain number of drops of a reagent to change the water sample back to clear. This test is often beneficial for those who cannot see colors properly.
OTO kits, though least expensive, are rarely used and not recommended because they measure only total chlorine—not free chlorine. Checking your free chlorine level is crucial because it indicates the amount of sanitizer available to kill bacteria and algae.
DPD kits, which cost about $30 to $50, measure free chlorine in addition to other parameters. To get started, pool owners take a water sample and add a set number of drops of a reagent. The reagent turns the water a certain shade, which pool owners then compare to the color blocks provided to determine their swimming pool’s current levels. When used correctly, DPD kits can measure certain parameters that test strips cannot. However, they’re not as convenient to use, and there is often greater chance for human error if you add different-sized drops or the wrong number of drops, which will affect results.
What to Test For
Experts recommend checking sanitizer and pH levels daily, and measuring alkalinity and calcium hardness once a week. Keep in mind that pH, alkalinity, and calcium hardness (not total hardness, which also includes magnesium) levels make up the water balance, and each one of those levels affects the others. Check the label carefully to know exactly what parameters the product is testing.
Basic test strips (often called “3-in-1”) typically measure sanitizer, pH, and alkalinity. More advanced strips (such as “7-in-1”) can measure free and total chlorine, bromine, total hardness, and cyanuric acid. Basic test strips are suitable and affordable for daily testing, but more comprehensive testing should be done once a week with advanced test strips or a DPD kit, or at least once a month by taking a water sample to a swimming pool supply store. (Most stores offer free water testing.)
Since test strips can measure total hardness, but not calcium alone, pool owners should use a combination DPD test or take it to a professional to obtain the calcium level. Calcium hardness lets you know if the water may cause scale or corrosion.
Storage and Shelf Life
“Heat and moisture can degrade test kits and lead to inaccurate readings,” says Jon Brew, business unit director for AquaChek, a line of test strips and digital readers, located in Elkhart, Ind. Extensive sunlight also tends to fade the color comparator used for test strips, so keep them off the swimming pool deck. “Storing reagents in your shed isn’t a good idea either because it can get very hot and humid. Keeping them in a safe place in the house is preferable,” Brew says.
Use testing products up to their expiration dates—generally between 18 months and two years after purchase—but consider purchasing fresh products at the start of each season if the strips have been exposed to harsh elements.
A Second Opinion
Swimming pool specialists recommend taking a water sample to a pool supply store once a month (and anytime the water seems problematic) to obtain a more comprehensive reading. You may get the same results using an in-depth kit at home, but it’s good to have an accurate comparison. Stores can do specialty tests for metals, algicide, and other levels so you don’t have to buy a whole kit.
When gathering the sample, fill and cap it underwater to ensure no air gets inside, which could alter the chemistry. Take it to the store directly, and don’t leave it sitting in a hot car.
Producing Accurate Readings
Water Test Tips
For the most accurate readings, and that crystal clear water everyone admires, follow these time-tested tips:
- Read the label for each product, and follow directions carefully and in order.
- Wait the specified number of seconds for the test strip color to appear before comparing to the color comparator.
- Dry your hands before reaching into a test strip bottle to avoid altering the remaining strips.
- If you’ve just treated the water, wait to retest until the specified amount of time has elapsed—typically one filtration cycle.
- To fill your water sample console, insert the chamber upside down, then turn it right-side up once your elbow is submerged. This ensures you have a sample from well below the surface.
- Use the specified volume of water. The lowest point of the meniscus should rest at the fill line.
- Don’t test water near the return line, as it could result in misleading sanitizer levels.
- Take a sample midway between the shallow and deep ends of the swimming pool.