Mixed chlorine results between quick test and "drop"


Mar 12, 2008
Putnam Co., NY
I'm new to testing my own water and am using the TF-100. It's all straightforward but I'm getting mixed chlorine results. The daily "yellow tests" gives me a TC of around 3 and the R-870 shows a pretty consistent 4.5 to 5.0 FC and 0 to 0.5 CC. I took my last test to the pool store to verify and they show 3.6 for FC and TC. All my other results were pretty close to theirs. Any tips on closing the gap/getting closer results? I have a SWG so I'm not sure if the difference is a big deal but don't want the chlorine too high (I've got little kiddies that can't wait to get in the pool).

Thanks for any help. This site is Great!!!

My Test
FC 5.0
TC 5.0
PH 7.2-7.5
TA 90
CH 110
CYA 45

Pool Store
FC 3.6
TC 3.6
PH 7.2
TA 84
adj TA 69 (any idea what the diff is?)
Tot. Hardness 79
CYA 50


TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
Silver Spring, MD
I would believe the FAS-DPD test, it is more precise and more difficult to do wrong. I find the OTO chlorine test (shades of yellow) to be difficult to read between 3 and 5, anything in there looks like three to me. Also, it is not uncommon for some of the chlorine to "vanish" on the way to the pools store, which could account for their result.

You don't need to worry about adjusted TA. We don't normally use that around here. It is only important if you are trying to calculate LSI, which you have no reason to do.