I'm not sure what your question is. If you mean will the accuracy of the CYA test be affected by chlorine levels over 3 ppm, then the answer is no. Has someone told you this is true?
The reason for asking is that while in the pool store I noticed that there were some CYA measurement tablets (I use liquid to measure) that stated that the Chlorine level should be 3 ppm or lower for an accurate measurement.
The only dependable method for measuring your CYA from a pool service standpoint is by using the turbidimetric test (liquid test). No amount of FC will interfere with the turbidimetric test. The only thing that I am aware of that has been known to interfere with the CYA test is cold water tempertures.
Actually, I believe I read somewhere, maybe an article by John Wojtowicz, that the chlorine bound to CYA would not form the melamine-cyanurate complex that is what results in the turbidity in the CYA test. Usually, the FC level is too low to significantly effect the CYA test, but if one wants to play it safe, then one can add some thiosulfate (2 drops of R-0007 should be sufficient) to the pool water sample and mixing before adding the CYA reagent.
It might be interesting for someone with a pool at high FC levels, perhaps from shocking, to do a CYA test both ways. With this high an FC level, probably 5 drops of thiosulfate might be needed.
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