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 more accurate 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."
"The only other interference I'm concerned about nowadays has to do with water coming out of treatment plants," adds Seechuk. "Water treatment plants are limited in the amount of trihalomethane, or THM, that can be in water. THM is a carcinogenic substance that is in all water, and it comes from a reaction of chlorine with substances that are in water like humic acid. The limit is 60 ppb, though it used to be 100 ppb, and the EPA tests for this all the time. But treatment plants found that if instead of using free chlorine they use some combined chlorine to treat water, it wouldn't form these substances as much. So all around the country for the past two to three years, water treatment plants have been switching to combining ammonia and free chlorine in the distribution line.
"Of course, combined chlorine is not as good a sanitizer as free chlorine, so they have to use more, and so typically they're pumping out levels of 2 to 4 ppm of chlorine. And now the pool owner who fills his pool with water from the hose instead of getting it trucked in has got combined chlorine before he even has a chance to get in the water. And he's wondering where it's coming from, and he takes it into the pool guy and he's wondering where it's coming from. Filling a whole pool like that becomes a major difficulty, but even if you're using make-up water that has combined chlorine, when combined chlorine gets above 0.5 ppm, it winds up reacting as free chlorine in the test, so that's another interference. There is a reagent that gets that out, but the bottom line is higher levels of combined chlorine can break through and read as free chlorine, so you have to be aware of that."
3. START THE SWIM SEASON WITH FRESH REAGENTS, STORE TESTING MATERIALS PROPERLY AND REPLACE MISSING INSTRUCTIONS OR ANY BROKEN, FADED, OR STAINED EQUIPMENT.
"Reagents are perishables," says Ivusich. "Just like a head of lettuce or the pills in your medicine cabinet, the chemicals in a test kit or on a test strip pad will degrade over time, even under optimum conditions. The process of deterioration speeds up when storage conditions are not ideal. Extremes of heat and cold, as well as prolonged exposure to air, sunlight, humidity, moisture and treatment chemicals, will diminish their useful life. You won't get accurate readings with deteriorated reagents or with stained test cells or faded color standards."
Believe it or not, people still make the mistake of storing test kits near treatment chemicals. Seechuk recalls visiting a hotel pool in Arizona where the test kit for the pool was stored right above numerous canisters of liquid bleach. "Liquid bleach tends to evaporate out of its containers and one of the reagents in the kit contains potassium iodide, which when it reacts with chlorine becomes iodine," says Seechuck. "So when I opened up the kit, the first thing I smelled was iodine, and I said, 'I don't know how you're doing your tests, but whatever results you're getting are incorrect.'"
Jaunakais points out why it's important to store test strips in a cool, dry place. "Test strips are hydroscopic, which means they absorb moisture, and so these reactions commence and color development occurs based on moisture. So if you have test strips sitting next to a pool, and it's hot and humid, you could have additional moisture content being exposed to the test strips, which could deplete the amount of reactivity of the product and cause a skewed result."
Also, be sure to grab test strips with dry hands, notes Jaunakais, because if moisture from your hands gets into the bottle and onto the bottle and onto th strips, the strips may have less reactivity.
4. WHEN YOU DO REPLACE REAGENTS OR LABWARE, DON'T INTERCHANGE PRODUCTS FROM DIFFERENT MANUFACTURERS OR — EVEN WITHIN ONE MANUFACTURER'S PRODUCT LINE.
"Each manufacturer makes its reagents in different concentrations," says Ivusich. "Their color standards are developed for specific reagent concentrations and the view depths of test cells are also highly specific. For instance, Taylor produces several different phenol red solutions for pH testing and a different type of color comparator is used with each. The exception is that DPD liquids and tablets can be interchanged in most visual color-matching chlorine/bromine tests."
5. WORK WITH A WATER SAMPLE THAT'S REPRESENTATIVE OF CONDITIONS IN THE POOL AS A WHOLE.
Ivusich explains why this is so important: "If a pollster wants to learn if Americans support longer school days and he only asks students, his results will be misleading. If he only asks teachers — another special interest group — his results also will be misleading. In fact, the pollster will follow a strict protocol to make certain his report reflects the opinions of a wide swath of the public. Water sampling is like polling in that you don't want to base your assessment on atypical answers. For instance, water chemistry at the surface of the pool is atypical — it's interacting with the air's chemistry, evaporation is taking place, and it's where oils and debris float. Water chemistry at a return line, makeup water inlet, or chemical feeders is also atypical, since treatment chemical concentrations are different in these locations than in the pool at large. Also, water drawn from corner locations may not have experienced the mixing action open areas have. To get a representative sample, draw the water from mid-pool or test at both the shallow and the deep end then average the results. Grab your sample from at least elbow depth. Then test the sample immediately so that its characteristics do not have time to change."
In addition to getting his water sample from 18 inches below the surface and away from any return outlets, Dan Gossage, owner of Dan's Pool Service in San Antonio, Texas, and president of the San Antonio IPSSA Chapter, also tests water three times, not just once. "I do this to get a mean, or average, of the tests, and then use that data in order to make decisions on chemical additions," he says. "I'm more comfortable with that."
If you're not able to test the water sample immediately, it needs to be handled with care, says Joe Sweazy, technical sales and services manager for Hach Company. "First, the person collecting the sample should take care to minimize the amount of air inside the sample container," he says. "This is done easily by submerging the sample vessel, shaking it to remove remaining air and capping it underwater. Additionally, the sample should remain close to the temperature of the source in order to get a representative reading. Usually this means getting the water sample to the testing equipment quickly after it has been collected. Samples that have not been treated carefully will not accurately represent the customer's water, and therefore will not allow the pool professional to make accurate treatment recommendations."
6. START OUT WITH THE CORRECT SAMPLE SIZE.
It might take a little extra time, but if you need 10 milliliters of water for your test, start with 10 milliliters. "If you get too much, then you need to flick some water out of the tube, and if you flick too much, then you've got to get another sample," says Seechuck. "A lot of guys get frustrated with that and say, 'It looks close enough,' and they go ahead and titrate even though they don't have the exact amount of water they need."
7. GET A FRESH SAMPLE.
"Always grab a new sample of water for each different test you run," says Jaunakais. "Because, as an example, if you're using one of our DPD reagent strips, it actually releases chemicals into the solution. So dipping the strip over and over in the same sample could give you inaccurate results."
8. MAKE SURE DROPPER BOTTLES ARE DELIVERING THE RIGHT AMOUNT.
"With time and use, if the dropper bottles are rolling around in the case, the tips of the bottles can become electrostatically charged," says Seechuk. "And instead of delivering the 24 drops per milliliter it should, you could get more like 30 or 40 drops per milliliter, and that is going to affect your outcome. So what we recommend is if you think your dropper is delivering the wrong size, then take a moist cloth and wipe it off and that will hopefully get rid of some of the electric charge and get your drop size back to normal."
9. HOLD THE DROPPER BOTTLE VERTICALLY SO THAT THE DROP SIZE IS CORRECT.
"I always see guys holding it horizontally and adding drops that way," says Seechuk. "I always question them, and they say, 'I've been doing it this way for years.' Well, it's going to deliver a different drop size [when held horizontally] because it tends to cling to the side of the tip and it makes more reagent get delivered."
10. CONDUCT COLOR-MATCHING TESTS IN NATURAL DAYLIGHT OR WITH THE AID OF A DAYLIGHT SIMULATOR.
"Anyone who has ever walked out of the house wearing two pieces of clothing that looked liked they matched until they got in the daylight knows about this problem," says Ivusich. "The term for the phenomenon is metamerism. Different light sources make for different colors. If a test is designed to be read in daylight (after all, pools are mostly outdoors), then artificial lighting, i.e., incandescent and florescent, will affect your color perception. Sunglasses do too, so you'll need to take them off when running tests."
Test Questions?
Thoughts on NPIRC research results
During recent protocols conducted by researchers from the National Pool Industry Research Center (NPIRC) at the California Polytechnic State University in San Luis Obispo, researchers found some water test kits yielded inconsistent results, especially when testing for calcium hardness and total alkalinity. This may leave you wondering: Should I be doing anything differently when testing water. Or should I be using a certain kit. If you currently follow instructions provided by your test kit supplier, then, no, at this time you probably shouldn't change what you're doing. Dan Gossage, the IPSSA liaison to the NPIRC and owner of Dan's Pool Supply in San Antonio, Texas, hasn't switched test kit suppliers, staying with one he has used for years. And since he follows the manufacturer's instructions "to the T," he hasn't changed how he tests water, either, except that he is now doing three tests and averaging the results instead of doing just one. "Although, most of the time the result is exactly the same each time," says Gossage.
"However, I am very concerned about the calcium hardness data and cyanuric acid data because both of those parameters obviously affect what you're putting into a pool," Gossage adds. "I'm fortunate where I live and where my company is located that we have very high calcium hardness and quite high total alkalinity in the fill water going into pools, so we don't have to use a lot of increasing-type products. So I'm not as concerned as those probably in Northern California and Northern Texas where their values are very low out of the tap, and they're having to add calcium hardness increaser upon startup."
To account for any potentially inaccurate test readings, Gossage says he has "been erring on the side of high in regards to my pH and my total alkalinity. I would rather remove scale from a swimming pool — I'd rather be scrubbing tile — than to have a low pH or low total alkalinity, which would result in damage to equipment in a corrosive condition. So I'm sacrificing the scaling condition — even though the pools are not scaling — and I'm keeping them as high as I can keep them comfortably.
"I also tell everybody: Use a sequestering agent in order to prevent the precipitation of metals out of the water, and that's really your best insurance policy right now."
–K.E.
