Cyanuric Acid and correct Chlorine Levels

Problems relating to pH and total alkalinity.
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Cyanuric Acid and correct Chlorine Levels

Postby Womble » Mon 04 Feb, 2008 21:52

I am trying to understand why the recommendations for Chlorine based on CYA levels seem to contradict other recommendations.

I have been told and read in many places (including the side of my chlorine bottle) that the FC in my pool should not exceed 5ppm while being used.

Yet the Target FC recommendation for a CYA of 70 exceeds this significantly (8.1ppm) as seen in this chart.

I understand (although understand is a loose term) that a part of the FC binds with the CYA, which makes the FC less effective at higher levels of CYA is this FC not of issue and therefore excluded from the 5ppm limit?

Should I reduce my CYA to say 30 so that my FC levels can remain under 5ppm recommendation that is printed in many locations?



chem geek
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Postby chem geek » Tue 05 Feb, 2008 00:48


It all depends on who you want to believe. The chemistry of chlorine and CYA was figured out (equilibrium constants determined) back in 1973 and I've written up technical details about it and a spreadsheet doing the calculations in this post (the link to the spreadsheet PoolEquations in a ZIP file is near the end of the post). However, the industry doesn't make recommendations based on this chemistry.

If you have higher CYA levels then you can have higher FC levels. The 5 ppm FC absolute isn't important, but if for any reason you wanted this lower FC level then you would need to either have a lower CYA level or use an alagecide, such as a weekly dose of PolyQuat 60, to prevent algae.


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