Overshot CYA target - advice?


Well-known member
Jun 21, 2019
Louisville KY
Hi, I'm on year 3 of TFP-ing. The first two years I had a CYA at just 30 and had a hard time maintaining it there, adding a bit more mid summer. This year I thought hey, I'll add an extra pound and a half to make up for the loss in the cartridge or wherever it went. There was always the missing 10% or more. I always used sock-in-front-of-skimmer method with me squishing the sock/bag every hour or so. This year, I recently opened at 0 CYA, adding the target CYA using Pool Math plus extra, did the sock/bag thing, but started late in the day. I didn't want to leave the bag hanging in front of the skimmer overnight without the pump running and so I moved it to a 3 gallon bucket to 'rest' overnight, then the next day finished the job. I noticed the CYA was coming out much easier and seemed to be more dissolved overnight, as expected.

It's been a week, plenty of time to dissolve what might be left in the filter, and lo and behold - my CYA is at 70! I got a 60, 65, 70, 75 depending in the sun or shade. I tested a lot because I simply did not believe it. I should add that I AM using a different brand of CYA from Menards (Utikem brand), not the typical from Wal-Mart (Clorox I think).

A few questions -
Do you think the brand type changed the % dissolution of the CYA? Is the brand variability enough to matter?
Do you think that leaving it in the sock in a bucket of water overnight helped change the % overall dissolution? Or, just the rate.
My plan is to just ride this out this summer at 70, sucking up having to keep it at 8 instead of 5. (Will this cost more in terms of added Chlorine? Or does it even out given I am adding about 3-4 FC per day regardless of whether CYA is 30 or 70?)
Or, should I drain a few inches, add fresh water, or just know that we only have 2 more months of pool time left and it will all disappear over the winter?



Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
Laughlin, NV
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
If cyanuric acid, all brands should give the same effect. Based on you weighing out what you needed.
The bucket over night had no effect.
Your FC usage will essentially be the same. Just be diligent to not go below minimum.
Rain, high water temperatures, etc will lower it some over the next month or two.
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Well-known member
Jun 21, 2019
Louisville KY
Thanks Marty. I still really don't get how it's so high. I just ordered new reagent to re-check. I measured the target 7 pounds of CYA based on four, 1.75 lb bottles. I then eyeballed an extra 2 pounds from a canister from last year based on volume. I would have needed to add almost 10 lbs to get CYA to 70 according to the spreadsheet, and I really did not add that much. In the future I will have to go back to measuring only enough to get to say 40 and no more. And deal with adding mid season if needed. This is so frustrating because I am usually so careful with everything and the ONE time I take a change with the estimating it goes south. I'll have to accept it for now.
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