CYA levels in Southern California


New member
Jun 23, 2010
Hi, I'm hoping someone could comment on my dilemna.
My pool chlorine disippates very rapidly, by morning I usually show hardly any chlorine (using a standard pool chlorine 3 way test kit). I seem to constantly get some algae growing on the side of my pool walls.

The neighborhood pool supply store owner (he also has a pool service) claims that I need to bump my CYA reading to 100 PPM (I'm in southern california, inland) where currently its very hot and sunny.

My CYA reading is about 40 PPM right now..

Some other people in my readings have alluded to Southern California needing 100 PPM CYA, however this statement CYA 100 ppm in southern california) contradicts totally what most forum postings say, basically that too high of a CYA is bad.

Can someone in Southern California tell me if 100 PPM CYA is bad or not?

Thanks very much.


LifeTime Supporter
Nov 18, 2009
Sacramento, CA
You could bump you CYA to 50 if you want, but something you said concerns me:

v0520 said:
by morning I usually show hardly any chlorine
You should be losing less than 1.0ppm overnight. You your overnight loss is greater than 1.0 than you need to shock.

Post a full set of numbers to give us a better idea of what is going on including FC and CC.


Well-known member
Apr 26, 2009
Northeast Ohio
Welcome to TFP!!

I understand you want to hear from the Southern California folks and I'm sure several will be along, but I don't think raising your CYA to 100 ppm is going to help you. I would suggest doing an overnight FC loss test using a good drop based FAS-DPD test kit like the Taylor K-2006 or TF-100. If you're losing chlorine where there is no sun on your pool, it's an organic problem and you need to shock. Shocking your pool at 100 ppm CYA is pretty close to impossible, at your CYA level of 40 it's pretty easy.

If you don't have an overnight FC loss, then bumping your CYA up some could help, but to 50 or 60, I doubt anyone is going to suggest 100 on here.

While you wait to hear from the SoCal crowd, you might want to do some reading in Pool School and consider a good test kit to allow you to do an overnight FC loss test.


LifeTime Supporter
Nov 18, 2009
Sacramento, CA
...and if you have algae you need to shock anyway

By the way shock is a process not a product. Check out the link in my signature.

How do you chlorinate? What is your target FC level?

How much direct sunlight does the pool get?


TFP Expert
LifeTime Supporter
Jan 6, 2010
San Dimas, CA (LA County)
100 is too high.

Sounds like you can't keep enough chlorine in there to totally kill the algae, so it of course uses all the chlorine. Which means SHOCK. And shocking is easier with lower FC. Once it's all dead, the chlorine only has to fight the sun.


TFP Expert
LifeTime Supporter
In The Industry
May 20, 2007
SWSuburban Chicago, IL
I agree with the above advice...
You need a better test kit, one that includes an FAS-DPD chlorine test.
Test Kit Comparison

A CYA of 50 is good for So Cal, you could go to 60 if you want, but just know that the higher the CYA level the higher the FC must be - refer to the chart. It's not clear how you chlorinate your pool now, are you adding manually, in the evening/morning?

Ruling out organics consuming the chlorine via an Overnight Loss test would help pinpoint the problem but if you are seeing visible algae then you should probably shock the pool, and then make sure you stay above your "min" FC level at all times in the future and you should see your FC demand level off. Make sure you are using your "target" level for adding chlorine so that the FC doesn't drop below the "min".

How to Chlorinate Your Pool

Shocking Your Pool

Overnight FC Loss Test

Post back if you need clarification on anything! Hope this helps :)

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