photo of pool chemicals

Accurate water testing is one of the cornerstones of effective pool and spa service. After all, it’s impossible to properly treat water if you don’t know sanitizer residuals, pH, total alkalinity, calcium hardness and other key constituent levels.

The good news is that test kit manufacturers have spent decades perfecting their kits and procedures and these days, if you do follow the instructions to a tee, or close to it, you’re very likely to achieve reliable results.

The problem, of course, is that some people either ignore the instructions altogether and never have a firm grasp on how to achieve accurate readings, or, perhaps more commonly, fall into bad habits or take shortcuts.

To help servicers stay on the straight and narrow, we decided to revisit some testing basics based on input from technicians and manufacturer recommendations. The following can serve as a good refresher on test procedures for experienced techs who may have become a little bit careless, or as a tool for training novice technicians.

General Advice

First and foremost, it’s important to read and embrace the test kit instructions included with each kit. And keep in mind that although reagents may look similar from one test kit to the next, the color standards in the color comparator or color chart included with the kit can vary from one manufacturer to another.

It is also important to realize that reagents or procedures are not interchangeable from test kit to test kit.

The other general recommendation is to learn water chemistry basics along with proper test kit use. Accurate test results are critical, but so too is knowing what those results actually mean. Testing provides a window into water conditions in terms of sanitizer levels, water balance, organic levels, total dissolved solids, cyanuric acid levels and other important facets of water quality.

Obtaining accurate readings is in essence the gateway to proper management of a broader set of water chemistry issues, but you have to know how to interpret those results.

It’s also important to be aware of the differences between some types of tests. For example, an OTO test will reveal total chlorine, while a DPD test will give you a measure of free available chlorine, combined chlorine and total chlorine.

It’s common for service on low-use pools to use OTO because total and combined chlorine levels will likely be less important in those settings. For high-use pools, be they commercial or residential, a DPD test will indicate combined chlorine levels, which can be critical in determining whether or not you need to shock the pool or even drain and replace some or all of the water.

Be sure you know what you’re testing.

Please note: these measures focus on reagent test kits. Test strips, electronic meters or in-store testing centers are beyond the scope of this discussion.

Specific Recommendations

As you’ll notice, most of the following recommendations come down to basic common sense. Test kit manufacturers and experienced service techs point out that water testing for pools and spas is not difficult, so long as you follow these simple measures.

• Keep it clean: Accurate test results begin with keeping your test kit clean. The test tubes should be rinsed before every test. Unclean tubes and vials can result in staining or discoloration of the tubes, which can skew readings. Water or reagents remaining from a previous test can also distort readings.

Also, never cap a test tube with your finger. Oils and other matter on your skin can distort results. Use the cap that comes with the kit.

• Sample collection: Manufacturers recommend collecting samples from 15-18 inches below the water’s surface, basically elbow deep for most people, to avoid the oils and other materials that are commonly on the surface. In addition, stay about 6 inches away from the pool walls and avoid collecting samples from areas near returns, which may have higher concentrations of sanitizer or acid.

Also, be sure the system has been running prior to the test so the chemicals are properly mixed throughout the pool or spa. And avoid taking samples from known “dead spots” such as steps or corners, sun shelves or beach entries.

Always test the water immediately after collecting it. Chemical values can shift in water that sits in the test tubes. Finally, never test water immediately after a shock treatment.

For best results, the water analyst should take water samples from more than one area around the pool, particularly in larger pools.

• Be precise: Always hold reagent dropper bottles vertically and squeeze gently to obtain a uniform drop size. Never hold dropper bottles at an angle. Inconsistent reagent application will definitely impact results.

Having the precise amount of water in the test tube is crucial. Keep in mind the water’s surface tension will form what is known as a meniscus, a small raised contour around the edges of the sample. That’s why it’s always important to fill test tubes so the bottom of the water line is precisely on the indicated “fill-to” line.

• Fresh reagents: Keep reagent bottles tightly sealed and avoid excessive heat or freezing. Also, replace reagents that have passed their expiration date. As a rule, liquid reagents should be replaced every year.

Do not store reagents in direct sunlight or next to water treatment chemicals, which could destroy instructions or even slowly deteriorate test kit components.

Also, do not directly handle reagent tablets and avoid contact with liquid reagents.

Safety tip: Some chemical reagents are toxic, so it’s always important to store test kits out of reach of children.

• Reading the results: When using a color comparator, always read test results against a white background. It may be necessary to hold a piece of white paper behind the comparator when reading results. This procedure will neutralize background interferences, which can significantly affect test results.

Some service techs point out that reading test results while wearing sunglasses can distort readings depending on the color of the reagent test and the tint of sunglass lenses.

Due Credit

The adjoining set of testing recommendations is based on input from manufacturers LaMotte and Taylor Technologies.

We also had help from Bob Foutz, Jr., a Southern California-based service technician who has been working as a service technician for 30 years for both residential and commercial clients and Steve Kenny, a servicer and builder working in both the commercial and residential markets throughout Long Island, N.Y. and elsewhere.

Comments or thoughts on this article? Please e-mail editors@aquamagazine.com.