testing methods


Well-known member
Apr 2, 2007

I read on the forum that the FAS/DPD testing was the preferred method for testing the water. I bought a testkit from Leslies last month. I also get the water tested at Leslies until I get a comfort level with my testing. They use the OTO method. Does anyone know the differences? Disadvantages? What does it stand for?

Probably one disadvantage that I see with using the DPD method is the cost of the reagent R-0870. Does anyone know of any other place that is less expensive? Thanks in advance,

The Mermaid Queen

TFP Expert
LifeTime Supporter
Mar 28, 2007
Northern KY
OTO tests only Total chlorine. Fine for day to day maintenance, but relatively useless if you are having a problem. OTO also only goes up to 5ppm. OTO stands for orthotolidine, the yellow reagent used for testing

FAS-DPD tests FC and CC. you really need to know your CC if you are trying to clear up a problem. I beleive the FAS-DPD tests also accurately test up to 20 ppm, which is necessary if you are shocking your pool, or running a higher CYA level.

FAS-DPD stands for Ferrous Ammonium Sulfate-Diethyl-P-Phenylene Diamine, the reagents used in that test.

Most here test daily (or so) with OTO since it is cheaper, and test weekly or even monthly with FAS-DPD just to ensure things are right. Of course if you are having a problem, the FAS-DPD will be much more informative.

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
San Rafael, CA USA
A couple of additional points. The OTO test will not bleach out at high chlorine levels, unlike the DPD test (but the FAS-DPD test is also fine and doesn't bleach out though above 25 ppm FC it may turn brown and require additional powder to be added). The FAS-DPD test can be used up to 50 ppm (with the caveat of using additional powder as mentioned).


LifeTime Supporter
Mar 28, 2007
Richmond, Va
Okay, so I have the test kit from Taylor.........read the booklet, being not a chemist, but a social worker, I confess to being totally lost. What goes where and how many drops of what to which tube....etc. :?: :cry:

Got the pool opened up today and it looks pretty good. Some white powdery spots on the bottom that the guy said could be left over winterizing chemicals or dead algae. Vacuumed that to waste and pool is being filtered now. Will take water sample to pool store in the morning and also try to sort out how that water kit works! Water looks pretty clear, I am so relieved that it is not all green.