Often, dealer pool water testing isn't as accurate as the testing you can do
(It's worse than I had thought: see the note below.)
Chlorine, chloramines, pH, and alkalinity levels in your swimming pool water can change significantly between pool and store. Plus, the complex test apparatus some dealers have is more subject to operator errors than a simple home pool kit -- especially when that operator is an briefly trained college student home for the summer. Swimming pool test strips, which have begun to be widely used, are too imprecise for the job, even when used correctly.
Test it yourself and save all those trips to your pool dealer! And, avoid all those "Oh, this might (but usually won't) help" chemical purchases.
Decent chlorine and pH test kits are less than $10. And for around $65 or so, you can perform ALL the swimming pool water tests that you might ever need! (testkit info)
By the way, don't be too impressed with the 'water analysis' computers many dealers have. The computer does NOT test your water. The college student, or whoever, does all the testing, and simply types the results into the computer. Worse, in many cases, the computer program is mismatched with the testing method, and will virtually always recommend chemical addition, even when your swimming pool is fine!
It's worth keeping in mind that swimming pool water analysis programs were developed for the marketing departments of swimming pool chemical companies! (And you wondered why you always get a printout recommending that you add more pool chemicals!)
The material on this page was one of the first things I wrote, when I began creating PoolSolutions in 1997. Since that time, a lot of email from pool owners has passed through my server. And, I've found that the situation with dealer testing is worse -- in some cases, MUCH worse -- than I had realized. Some dealers do a good job, but many do not, and some are truly awful.
What's worse, swimming pool dealers who do a poor job of tesing your water have no incentive to 'clean up' their testing: the worse the job they do, the more chemicals they sell!
Just how bad can it be? Last summer (1998), one of my subscribers took three identical samples collected from her pools to one of the largest pool dealers in Arizona, along with two friends. Each of the three of them turned in one of the sample, as if it were from three different pools. The test results from each sample was totally different from the other two, even though each sample was collected from the same pool, at the same time, and from the same place! As a result, the chemical recommendations she received, based on each individual sample, were also totally different!
With the increasing use of the easy to use, but wretchedly imprecise, swimming pool test strips by dealers, the problem is likely to become even worse.
In many areas of the country, testing your pool water yourself is the only practical way for you to protect yourself against against computerized recommendations to use chemicals you don't need. You do need a reasonably accurate and precise swimming pool test kit. (testkit info) By testing it yourself can you determine whether your dealer does an acceptable job of water testing, or not!
If you have three or four dealers in your area, you can also do comparative sample testing: take an identical sample to each dealer, and see what results they get. Be careful to collect the samples in CLEAN sample bottles, at the same time, from the same place in your pool. Cap the bottles underwater so no air space is left, and take the samples promptly to the dealers. Generally, if two or more dealer test results agree closely, both are correct. If NO dealer test results agree, one may still be correct, but only your own test results will reveal this.
Some of you -- the fortunate ones -- will find that your dealer is doing a great job. Some will find your dealer's testing is OK, or at least, it's OK so long as a particular person does the work. Unfortunately, many will discover that your dealer's results are atrocious, and are a major contributor to the yard-long printouts recommending that you buy, and add, a dozen different chemicals to your pool.
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