My CYA disappeared!

Quant

Member
Apr 9, 2018
21
Gilbert, AZ
I tested CYA when I opened the pool early spring (I think February) and I was up around 40 where I want to be in Phoenix. I used only liquid chlorine so I felt ok about never testing CYA until late July when I was burning through chlorine so fast I had to go into troubleshooting mode. I tested 0 CYA--- crystal clear water filled right to the top of the test tube. I did not believe it and ran down to the pool store and bought new CYA reagent--same thing!

The problem is fixed but I had to add 2 gallons of CYA back into it and started using some chlorine solids.

Bad on me for not testing CYA once a month or so--but where did my CYA go? My water bills have been normal all season so I can't see how I got all the way to 0 without me noticing a higher water bill? My water hardness has increased normally from opening, so that is more evidence that I have not been dumping/refilling fresh water into the system. If I had, I'd expect my hardness to also be around my tap water levels.

I thought the only way to drop CYA was to dump water though I seem to remember reading about some uncommon algae that eats CYA?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,445
Laughlin, NV
CYA degrades naturally in water by a very small amount. It does degrade quicker in elevated water temperatures and in high UV areas. I see about a 10-15 ppm loss per month in June, July, and August. Test your CYA monthly from May to September and every other month the rest of the year.
 

Quant

Member
Apr 9, 2018
21
Gilbert, AZ
CYA degrades naturally in water by a very small amount. It does degrade quicker in elevated water temperatures and in high UV areas. I see about a 10-15 ppm loss per month in June, July, and August. Test your CYA monthly from May to September and every other month the rest of the year.
Thanks, I had no idea. With that kind of loss, I think I could keep a stable CYA using tablets 3 weeks out of every month during the summer.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,445
Laughlin, NV
Up to you. For each 10 ppm FC added to your pool, 6 ppm of CYA is added when using trichlor (tablets).

So if you need 5 ppm FC each day in the summer, my average, you would be adding 3 ppm CYA each day you used tablets only.
 

Etchase

Active member
May 22, 2019
31
Hawaii
CYA degrades naturally in water by a very small amount. It does degrade quicker in elevated water temperatures and in high UV areas. I see about a 10-15 ppm loss per month in June, July, and August. Test your CYA monthly from May to September and every other month the rest of the year.
What CYA levels are you running at? I always thought the loss should be a percentage, but I lost 30 ppm in two months starting at about 50. There was a wild fire which put lots (an inch) of ash in the pool, which possibly had something to do with it.