Two Store test measures chlorine but 2 brands of home test strips do not. What?

[Sus]

I went to a local pool store to have my water tested. Their computerized test measures all chemicals in balance. Free chlorine 1.65. Total chlorine 1.65. Ph 7.2. Alk 109. Cyn acid 75. Pool temp 80. Live in PA. The pool store test involved measuring the water in several different vials and putting the vials in a digital reader attached to the computer. Water is crystal clear. Sand filter recently back washed. Sounds good, right?

Problem: htp brand and aqua check brand pool strips register chlorine level as zero. The pool store owner used both of these test strips at my suggestion in the water sample I brought and got the same result I got at home...chlorine reads zero on these strips. So Why do these strips, which for the past 5 years used to measure all chemicals correctly for me, they do not measure chlorine?

We even checked his computer test and compared it to a test involving testing the water with drops and comparing the water in a rectangular vial that had color test strip on the side of the vial and even this test showed the chlorine was fine.

So what do I do now?

 

[JasonLion]

Welcome to TFP!

Dependable accurate water testing is the foundation of pool care. None of those test results are what we consider reliable. Pool store testing is frequently wildly wrong, with the computerized systems usually being the furthest off. Problems with pool store testing are far more common than you might imagine. And you should never trust test strips.

Worse, what you call "in balance" is not even similar to what we call in balance. The FC level you report from the pool store is way way too low for a CYA of 75.

 

[Sus]

So what do I do?

 

[JasonLion]

Your best long term option is to get your own top quality test kit. A good kit, like the ones we recommend (see the Pool Chemistry section of Pool School), will give you better results than most pool stores right from the first day.

 

[Isaac-1]

First let me say welcome, second to follow up on what Jason said, many pool store computerized testers are designed to LOOK fancy and technical to give the impression that you should trust them, many of these systems are not so good in reality, although I will admit some may be getting better. However one of the key problems with many of these computerized tester is the simple fact they are out of calibration, as regular calibration to known good reference samples is an important step in most computerized testers. It is hard to say more without knowing the exact type of test setup this store has, however our suggestion is always going to be the same, ditch the test strips and buy one of the suggested drop based test kits in the pool school link in the upper right (I use the TF-100, see my signature for link as it provides the best bang for the buck). While you are reading pool school I would also suggest you read some of the other pool care chemistry articles like: http://www.troublefreepool.com/content/123-abc-of-pool-water-chemistry

 

[YippeeSkippy]

Just as an example of dubious pool store testing- Yesterday I needed a small part for my pool. Lately, when I have to go to a pool store for something I've been taking water in for the free testing. Just for the fun of it, to see what they say, y'know?
I tested my water and my CYA is 40 (I've been raising it up again slowly since Skippy accidentally drained a mess of water last month, oy!) and pool store #1 said my CYA was 27, and pool store #2 said 60.
If that doesn't convince you that pool store testing is questionable at best nothing will! (oh yeah, pool store #1 happily informed me my phosphates were 250 and for $50 I could buy a bottle of magic phospate killer and all would be well with the world....LOL)