Issue when testing chlorine with FAS-DPD kit.


New member
Oct 7, 2020
Tampa, FL.

We purchased the 2006 FAS-DPD test kit to more thoroughly test the pool water. However in comparison to the OTO test or results from Pinch-a-Penny the chlorine test always comes out to about twice as high. Meaning currently Pinch-a-Penny says the total chlorine is at 4ppm. The OTO test comes in between 3 and 5 but the DPD test measures 8ppm. And no matter how the chlorine level varies it always reads about twice as high.

I've tried testing both the 10ml and 25ml methods, purchasing new agents, using a magnetic stirrer, and using only one scoop of powder. Nothing appears to make a difference. All the other tests perfectly align with the Pinch-a-Penny results.

I also tried reaching out to Taylor but they basically treated me like I couldn't count drops. Is there anything I am missing that can be causing these results?


Gold Supporter
Silver Supporter
In The Industry
Aug 14, 2018
It looks like you are going to need a third reference. Do you know what method the store are using for testing? I would be more inclined to belive your own readings. The endpoint is pretty much final when using the powder.


Bronze Supporter
Jun 1, 2018
Hernando, Ms
Pool Size
Salt Water Generator
SWG Type
Intex Krystal Clear
Also remember not to squeeze the bottle- hold it straight up & down & let the drops come out via gravity ( this results in less but larger drops) vs squeezing & ending up with more but smaller drops. Adjusting this may account for some of the discrepancy. As everyone else stated- oto is not super accurate- its more of a “do i have any chlorine?” Type test. I would still trust your own results over the ps.
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Reactions: yann


New member
Oct 7, 2020
Tampa, FL.
@moore887, not sure what test the pool store uses. but I will find out.

I guess after using the OTO test for more years than I care to remember it's hard to believe there can be that much of a difference between the tests. Thanks everyone.
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