Bringing cya/chlorine down a notch


LifeTime Supporter
Jul 8, 2010
I am understanding that there is a working relationship between CYA and FC....the higher the CYA, the more FC you need....but in any case, I thought that pools with FC above 4 FC were not safe to swim in? So, isn't one required to lower the CYA to keep the FC requirement around the ideal 2.0 ppm and the pool swimmable? My CYA is about 60, and my FC is over 5, so I'm replacing some water, trying to bring everything this proper thinking? I did have some kind of algae in my pool, shocked it like mad, and my FC and TC are the same, so I think I've divided and conquered...once I get my CYA to about 40, I am switching over to bleach....


TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
Silver Spring, MD
No. The upper limit on FC of 4 (or often 3) is from long ago when people didn't use CYA. Once you have CYA in the water it is fine to have the FC level significantly higher that it can be when there isn't any CYA at all.

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
San Rafael, CA USA
For commercial/public pools, California has minimum FC requirements but no maximum FC limit in state regs (local regs may set such limits), Texas has a maximum of 8 ppm FC, New York has a maximum of 5 ppm FC, Massachusetts and Arizona have a maximum of 3 ppm FC, Florida and Wisconsin have a maximum of 10 ppm FC, while the EPA has a drinking water limit of 4 ppm (also shown here). The state limits are often higher than the EPA limit because the EPA limit is based on drinking water standards which do not account for CYA. Even the state standards do not fully account for the chlorine/CYA relationship since their FC and CYA limits are not related and are separate ranges (and New York bans CYA in commercial/public pools, for example).

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