Differences in test kits

[CanuckPool]

OK, can someone tell me the differences between a OTO kit/FAS-DPD/DPD/strip kit. I go to the pool store and try to figure out which is which, what is an easy way to tell one from the other... ok, I know what a test strip kit looks like. Also maybe a little enlightment on the accuracies of each.

[CarlD]

Odds of finding a FAS-DPD test kit at a pool store are minimal. Not zero, but close.

I found a FAS-DPD Monopersulfate test at a local Leslies a few years ago--it was a close-out and I got it for $19.95. Never saw it again.

Another Leslies in another state had a container of FAS-DPD powder. The kid running the store couldn't figure out what it was, and couldn't find a price on it, so he just gave it to me!

DPD and FAS-DPD tests that allows you to isolate the good chlorine (Free Chlorine-FC) from the used-up chlorine (Combined Chloramines--CC) and measure both.

An OTO kit only measures Total Chlorine (TC) which is the sum of FC and CC.


But FAS-DPD is highly accurate, measures up to 50 or even 100ppm, and uses drop-counting titration. That means you count drops you add to the solution until it goes clear. You can measure .5ppm or even .2ppm with FAS-DPD.

I haven't used DPD in a long time but I believe it uses color matching, which is harder to do. DPD usually tops out at around 10 to 15ppm, but has TERRIBLE disadvantage--very high FC levels can bleach it making it look like you have NO chlorine!

OTO is simple and straight forward but doesn't isolate out FC from CC. It usually tops out at 3 or 5ppm, but you can double or triple it by diluting your pool sample with distilled water (the CarlD ShotGlass Method).

Strips are very, very difficult to read accurately. Many times the TC shows lower than FC, which is impossible. They use color matching, are hard to match, and really should only be used as a quicky backup to indicate gross trends--Like "OHMYGOD! There's NO chlorine in this pool at all!" Or "You're gonna bleach your feet and melt your suit right off!"

FAS-DPD is the best way to test your chlorine accurately and completely.

[CanuckPool]

So the only way to get a FAS-DPD kit is by ordering online... ok, I get it now, thanks!

[CarlD]

So the only way to get a FAS-DPD kit is by ordering online... ok, I get it now, thanks!

The only way? Pretty much. Certainly the best way.