Understanding chemical readings

nonasdada · Jul 30, 2012

hi

This is the first year I try to maintain the pool chemicals. This is probably a stupid question, but here it goes

I recently got my TF-100 test kit. I am trying to understand the difference (if any) between CL and FC. When I measure Cl with the K-1000 set, I usually read between 2 and 3. However when I do the FC test, I get 4 ppm. CC is 0. So should FC and Cl be the same?

Also, is there a way to test exactly the PH. Based on the K-1000 set again, the Ph is usually between 7.2 and 7.5. i am just curious to know if I can find the exact reading somehow with the TF-100 kit.

The rest of the results are
TA 110
CH 230
CYA 20

Regarding the CYA reading, should the black spot disappear completely or is the reading to be taken when the black spot becomes grey?

We have a 22000 gallons pool, with a DE filter, and we just had it replastered.

Thanks. Callyann

jblizzle · Jul 30, 2012

There are extended test instructions in a sticky in the Testing Forum that should answer all your questions.

The OTO chlorine test measures total chlorine ... it is not really surprising that they do not match ... trust the FAS-DPD test.

That is the only pH test. Nothing more exact is available.

Dot should be totally gone and lighting during the test is very important.

Posted from my Droid with Tapatalk ... sorry if my response is short

nonasdada · Jul 31, 2012

Thanks Jason for your prompt answer.

From your answer I understand that FC is the FAS/DPD test and CL is the OTO test. However, you said OTO measures total chlorine but it reads as between 2 and 3 and as I said, CC with the FAS/DPD test is 0 yet FC is 4 ppm so it is still not making sense to me BUT as you suggest, I will trust the FAS/DPD.

Not sure what you mean by "......In a sticky in the testing forum". I don't know what a sticky is in that context.

Thanks for claryfing the disappearance of the black dot. Next time I will make sure I am in full light.

crek31 · Jul 31, 2012

Here is a link to the "sticky" referred to. Sticky is like an electronic post-it note and they are at the top of each index category.

extended-test-kit-directions-t25081.html

UnderWaterVanya · Jul 31, 2012

OTO is very subjective. Easy to have minor errors. FAS-DPD is more accurate.

nonasdada · Jul 31, 2012

Thanks everyone for your answers and link, very helpful

Mona · Jul 31, 2012

nonasdada said:
Thanks Jason for your prompt answer.

From your answer I understand that FC is the FAS/DPD test and CL is the OTO test. However, you said OTO measures total chlorine but it reads as between 2 and 3 and as I said, CC with the FAS/DPD test is 0 yet FC is 4 ppm so it is still not making sense to me BUT as you suggest, I will trust the FAS/DPD.

CC = combined chlorine and you want this to be .5 or less
FC = free chlorine
TC = total chlorine = FC + CC