Pool Test Kits

[CarlD]

Glenn,
I use strips, have excellent color perception (unusual for a male but even my wife acknowledges it) so that's not a problem, but I don't rely on them. They are the canary in the coal mine to me--early warning of a problem. That's because I cannot tell if my pH is 7, 7.2, 7.6 or 7.8 using strips. Also, strips max out on FC at 10ppm. If you need to shock to 12, 15, 20 or 25ppm, they are useless. For CYA, they are inevitably wrong, and the TC tab on the strip usually reads lower than the FC, which isn't possible.

With FAS/DPD you CAN read changes in FC or CC down to .2, but rarely will you ever. Most of us ALWAYS use the .5 scale. The ONLY time I have ever found the .2 scale useful is if I see a CC of .5 or less I can't seem to get rid of. Then I'll measure at the .2 scale and, inevitably, the CC reading is .2 or less, which IS trivial. But if it's higher than .2, but still lower than .5, I'll want to shock the pool before it becomes a problem.

There is a way to use OTO testing to read higher than 3 or 5ppm, which works (search for the CarlD Shot Glass Method, or CarlD Patented Shot Glass Method ) by diluting with distilled water, but accuracy drops with each level of dilution.

Carl

[chem geek]

Yes, I wasn't recommending using a 25 ml sample with 0.2 ppm precision and accuracy, but rather that you COULD be that accurate if you wanted to and that it says something about the quality of the test. Most people use a 10 ml sample for 0.5 ppm precision and accuracy which is fine in most circumstances. For my own pool where I find the 0.2 ppm resolution useful is in two situations: 1) when I want a better handle on the Combined Chlorine (CC) level which is always very low in my pool (i.e. I want to know more than just <= 0.5 ppm; I want to know if it's <= 0.2 ppm) and 2) when doing an overnight chlorine loss test since such losses are also low or even when doing a daytime loss test. These latter loss tests are useful for figuring out average chlorine demand to the point where I can even tell when my wife has peed in the pool (see this thread, for example).

[CarlD]

Richard,
You've just re-defined...TMI!

Carl

[PoolDoc]

Actually, I need to write a page about pool peeing and pool pee-ers. It's more common than you think and can have severe effects on water chemistry.

FYI, 95+% of USS swimmers have developed the habit of peeing in pools -- practices are too long for any other option.

Ben

[CarlD]

Not in my pool! I don't allow them to do that or swim in my toilets either!

My Father had a sign: "This is our OOL. Notice there is no 'P' in it!"