is there a reason to raise CYA above 30?


Well-known member
May 7, 2020
Lathrop, CA
CYA is like a sun block for chlorine, so higher levels will lessen free chlorine loss to sun exposure. Levels of 40 to 50ppm are recommended for pools that have lots of sun exposure and in the southern states where the swimming season is much longer than northern states. Higher CYA levels are also recommended for pools that have salt water generators.
The downside of higher CYA is that you have to keep the FC levels higher and if you have to perform a SLAM process, the slam FC level is also a lot higher. You also use more drops to test for FC as a result.
Refer to this Chlorine/CYA chart

In Portland I would expect 30ppm CYA to be plenty enough to protect chlorine from the sun.
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Bronze Supporter
Aug 2, 2017
SE Kansas!
would it keep my chlorine levels more stable or offer any other advantage?

i see ranges of ideal CY from as low as 20 up to 50.
If you are losing more than FC/4-5 from morning to night, but no loss overnight, that could indicate a need for slightly higher CYA/FC level. You'll have to track your pool and it's preferences :)
Keeping the CYA as low as possible for each pool allows for more manageable chlorine levels.


Active member
Jun 4, 2016
Portland OR metro
We have very long days in the summer here and almost no rain/clouds after 10 am so on a sunny day my pool gets 14-16 straight hours of sunshine. We have a 12 kW solar system which produces ~ 80 kWH daily for those couple months. That said I don’t know how it compares to a place like Texas or Arizona.

We are losing around 1 (cloudy day, no swimming) to 2 (sunny day, swimming) ppm per 24 hours so it sounds like we are doing ok with the CYA?
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