Fas-DPD, DPD, OTO - What is the difference?


Well-known member
Aug 1, 2010
Columbia, SC
Trying to make sense of all of this testing stuff. I have wound up with three kits, two are the ones that came with the TF100 kit and I have a Leslie's (Taylor's) kit that is labeled DPD but it is all drops (no powder).

Bama Rambler

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2009
SouthWest Alabama
The FAS-DPD is the best chlorine test out there that's available to most folks. It'll measure FC and CC to 50ppm. It is also the easiest to read as it goes from pink to clear and the endpoint. The OTO kit is good as a go/no-go kit. If you're not sure whether you have any chlorine or not you can use it to tell. It'll always turn some shade of yellow if there's chlorine present. I['ve never used the DPD kit so I can't comment on that.


Mod Squad
TFP Expert
LifeTime Supporter
Jul 10, 2009
Houston, Texas
The FAS-DPD test with the powder is the FC test that will tell you exactly what your FC and CC levels are when you count the drops and divide by .5 . That test is best to determine how much chlorine to add to reach a precise target level. There should be a small jar of powder (R-870) and a little blue scoop in your test kit. The R-871 drops are used for the FC level, then the R-003 are used with additional drops of R-871 to measure CC.

DPD and OTO are drop based only and give you a range result based on what color the solution is at the end of the test. Many people have trouble distinguishing the color shades to get an accurate reading, so those tests are used mainly to check for the presence of chlorine, rather than how much chlorine do I need to add to reach my target level.

You can check the contents of your TF 100 kit against the list of contents on the web site. tftestkits

Darkside of the Pool

LifeTime Supporter
Jul 20, 2010
Another little clarification. OTO doesn't ''Bleach out'' as DPD does. When chlorine is very high, OTO will form some precipitate... it will color orange or brown.

I use this to better guide my customers when fighting algae... using Di-Chlor first to get a reasonable stabilizer level, non-stabilized chlorine afterward and keeping chlorine high enough to get a ''false reading''. I still strongly recommand you (as much as I) to get an FAS-DPD test.

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