Testing water seems like it should be quick and easy. You just dip a strip anywhere in the pool water and read, right? Wrong. If you’re giving your customers the best service you can, you know it’s not that simple. In fact, there are a number of critical factors
to keep in mind as you test pool water, so with the help of a few industry experts, AQUA has compiled a list of 10 water testing best practices, which can help you obtain moreaccurate results.
1. FOLLOW THE INSTRUCTIONS.
Wayne Ivusich, sales manager for the pool and spa industry at Taylor Technologies, explains why this is so important: “Not only are each manufacturer’s tests different, sometimes a manufacturer changes a procedure. Take test strips. To get the proper exposure of reagent to water chemistry, you can be instructed to dip quickly, swirl the pads a specified number of times, or swish the strip back and forth. Dip when you should swish, and color development will be compromised. If the wait times to observe between readings have changed and you’re unaware, you will also get unreliable results.”
“A lot of people think, ‘It’s a test strip, they’re all the same,’ but that’s not true,” says Lea Jaunakais, vice president of Industrial Test Systems. “For instance, we have patents on some of our indicators, so we have very specific instructions for some of our products that are very different than any other product we offer and very different from any other product on the market.”
In addition, says Jaunakais, if you buy a new kit, read the new directions. “So many people get familiar with a certain test procedure, and then they buy a different product, but instead of reading the instructions, they use a similar procedure that they’ve been using for years and get inconsistent results.”
2. ACCOUNT FOR INTERFERENCES.
Even if you follow manufacturer’s directions to the letter, at times you’ll also need to consider and compensate for interferences. One of the most common interferences is bleaching of diethyl-p-phenylene diamine, or DPD. “This reaction depends on there being more DPD reacting than chlorine,” explains Tom Seechuk, marketing manager at LaMotte Co. “You want to have an excess of the DPD there, but in a situation where you have high chlorine, the opposite is occurring you have more chlorine and that oxidizes some of the DPD so that you don’t have more DPD than chlorine.
“So when you’re running a test, if you have a very high chlorine solution and you add DPD, you’ll get a pink color and all of a sudden it’ll start disappearing and then it’s a clear solution (this is the bleaching), and that usually starts occurring at 10 ppm or above. But below that, starting at about 6 ppm, you’re going to start getting some partial bleaching, so that even if you know there’s 8 ppm of chorine in there, it’ll only show 7. At that point you either add more reagent or do a dilution. The bottom line is you need an excess of DPD and when you don’t have that, the color that should be formed isn’t formed.”
Another interference Seechuk noted is one that can be experienced when using non-chlorine oxidizer. “If somebody wants to use the pool very quickly after shocking, instead of throwing a bunch of chlorine in there, you can throw in monopersulfate, which is a non-chlorine shock, and it does the same thing,” he says. “It turns out that monopersulfate reacts like combined chlorine, so you think you still have combined chlorine when you really don’t, but there is a reagent to get around that and you should use that.”