Is there a "correct" CYA?

[Tom.B]

Just wondering if there is an ideal range for CYA? I am at 50-ish now and have an urge to push it higher. However, I wonder if that's going to just cause me to use more chlorine for little or no reason.

Free Chlorine 6.5
Combined Chlorine 0.5
PH 7.4
Total Alkalinity 80
Calcium Hardness 160
CYA 50
Phosphates 125

[chem geek]

A higher CYA level even with a proportionally higher FC level (so constant FC/CYA ratio) results in a lower absolute FC loss per day. This may be due to some CYA shielding effect in addition to its protection by binding to most of the chlorine. So if you are in a sunny area with high FC losses, then a higher CYA level can help. The main risk to a higher CYA level is if you have to shock the pool if for some reason you let the chlorine level get too low and algae started to develop. The shock level would be proportionately higher at higher CYA levels so that means you would use more chlorine. So I wouldn't go any higher than 80 ppm CYA for that reason.

[FormerBromineUser]

ChemGeek knows his stuff!

In my non-technical world, I keep my CYA as low as I can. I base my CYA level on losing no more than 2ppm FC on a daily basis (maybe a tad more after a party in August...). If my daily FC loss was above 2 to 2-1/2, I would raise my CYA slowly and adjust all ideal ranges in proportion.

You don't mention how your testing is done. Phosphate reading makes me curious. I see you have a PF number...

[Tom.B]

If memory serves, I was losing 1.5 PPM of FC per day LAST season. I haven't tested that this season. Our pool doesn't get sun until about 11am and goes back in shade about 6pm this time of year.

So if I am understanding it correctly, higher CYA means lower daily loss?

[FormerBromineUser]

Not sure who you were responding to, but Richard explains it better than me for sure!

The primary reason for having CYA is to protect your FC from sunlight. If you get that much shade, you should be good keeping CYA lower.

[chem geek]

Yes, higher CYA with proportionately higher FC to prevent algae growth results in a lower absolute FC loss per day. However, it doesn't sound like you get full sun all day long so your losses are probably already reasonable so you probably don't need to go above 50 ppm CYA.