Swimming Pool Water Test

Why Do You Need To Test Your Swimming Pool Water?

In Blog, Chemistry by Cathy Erntson

For those working with pools and spas, the mighty water test is a big part of our daily routine. The results can make us stand back and smile upon our aquatic bodies, basking in the glory of a crystal blue mirror or send us into a tailspin of chemical additions and equipment troubleshooting, completely hijacking our day. And it all starts with a series of tests, most of which have become so routine in our lives we could perform them blindfolded. Or could we….

Where are you taking your samples?

On a commercial body of water, the chemistry can be vastly different between the pump room and the body itself so you should never be relying solely on readings you get from samples in the pump room. You want to know the chemistry of the overall amount of water, not the small portion in the pump room before making any adjustments.

When collecting samples from the deck, are you near return jets?

The water coming from the returns is freshly filtered and is carrying the sanitizer and acid back out to the body for Cl and pH control. That’s the kind of sample that will lie to you; give you false assurances and make you think you have more Cl than you do or make you think the pH is too low, forcing you into action.

How far down are you reaching into the water to collect your sample?

Even though we work in the AQUATICS industry, I have seen many techs behave as though their arm may melt off if they submerge it. As humans are not water soluble, this is very unlikely to happen. So yes, you should absolutely be rolling up your sleeve and going elbow in to collect the sample. The surface on any body of water is going to hold the highest concentration of contaminates and have a lower Cl level. (Due to the extra dirtiness of surface water it is commonly accepted that 75% of water removal happen at the surface!)

Once the sample is gathered, how are you handling the reagents?

When working with the reagents, you are making chemical reactions happen, thus leading you to your results. These are supposed to be precise, measured reactions giving you an accurate result. The common mistakes here are to a) hold the reagent bottle askew when dropping drops and b) not swirl the sample enough after each drop. How you hold the dropper bottle seems silly, but keep in mind that the formula and multiplier you use to get your end results are based on the number of drops you add. If there was no consistency to drop size, some people’s single drop might equal other peoples 3 drops, giving them different end results. The tips on the bottles are designed to drop a certain amount of reagent per drop, but this only works if you hold the bottle straight up and down. Tilting it off to the side can cause your drops to be smaller or larger than was intended. The difference between 6 drops and 3 drops can be the difference between thinking you have .6

Chlorine or 1.2 Chlorine. As for swirling, many times people just don’t even think much about doing it till they are a few drops in already…” Well I know I’m already at blank level so I can just drop in 5 drops and start from there”. You can overshoot your actual reading fairly easily by doing this loosey-goosey style of swirling. It’s simple and easy; swirl after every drop. Every. Single. Drop.

As much of a no-brainer as all of this article has seemed thus far, we constantly see the topic rehashed because of how often improper techniques are still being used. A few other tips for the getting the most accurate results out of your tests:

  • Anytime you work with color comparators, read the colors in natural light not fluorescent as this can influence the shade you see.
  • When filling the sample chamber, measure from the bottom of the meniscus. Water clings to the sides of the vessels we use causing the surface center to dip in. The bottom of this meniscus should even with the fill line.
  • Don’t cross manufacturers reagents. Just because they are meant for the same chem test does not mean you will be working with a reagent with the same formula as YOUR kit came with.
  • If reagents have frozen or been subjected to ungodly summer temps sitting on a sunny window, throw them out and get a new kit. The reagents can lose their effectivity and give you different results.

Great water starts with great chemistry. So roll up your sleeves and get your arms in!

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