Did Aliens steal my CYA?

[ride525]

Because of other stuff going on, I let my 28,000 gallon pool go farther than I thought this winter. Water was a very dark green, although not much leaves and debris in it, I've been vacuuming, and most, if not all, the leaves are removed. Still green for a long time even though adding a lot of chlorine.

Finally SLAMed it last night with 10 bottles of 8.25% bleach.
Finally found where my test kit was hiding and lowered ph to 7.4.
FC is currently 11, with CC at 0.
Tested and retested CYA (with new test chemicals) and result is a bit lower than 20, perhaps 15. Where did it go? I haven't tested it for a couple of years, as it's been about 90.

Anyway, pool water is looking much better, it's a very light green now. I actually did a search and found some postings from about five years ago, that said that the CYA may have created ammonia with all the dark green algae (and maybe bacteria) I had.

Any thoughts besides adding CYA? Suggestions for level to shoot for?

Thanks in advance for your thoughts.

 

[zea3]

Use PoolMath to determine the correct levels for your pool. Once you plug in your pool volume and current test results it will tell you everything you need to know.

 

[bridgman]

There seem to be more reported ammonia problems this year than before, although that may be a function of site growth as well.

The working theory seems to be a soil bacteria that converts CYA to ammonia (or other things)... symptoms are that you pour in a bunch of chlorine but it gets eaten immediately and your FC keeps going to zero without making a dent in any algae. Sounds like you may be past that anyways since your FC is at 11, if so that's great news.

General recommendation seems to be to take CYA up to ~30 for the SLAM even if you want it higher eventually. People in sunny areas (don't know exactly where Fremont is in CA but it seems likely to be sunny ) are being advised to keep CYA levels closer to 50 to reduce chlorine consumption, so maybe 30 for now and 50 after the SLAM ?

 

[jblizzle]

CYA drops due to splashout, backwashing, overflow, etc. It also drops very slowly just due to being broken down by the chlorine. It can also be broken down by bacteria in a swamp which would show up as high CC levels upon opening. Seems that maybe you should test it more often than every few years

 

[ping]

I doubt that ammonia is the cause for the low CYA level and jblizzle's explanation would be my first guess.

Bring the CYA up to 30 until you are finished with the SLAM Process.

 

[karmabiker]

Keep that slam going ( remember M is for maintain). ... And after adding the cya don't bother testing for a week. Assume the level you targeted is the actual level. It takes up to 7 days for the test to reflect the actual level.

 

[bridgman]

I doubt that ammonia is the cause for the low CYA level and jblizzle's explanation would be my first guess.

Yeah, I missed the "couple of years" part. Good catch.

 

[ride525]

Use PoolMath to determine the correct levels for your pool. Once you plug in your pool volume and current test results it will tell you everything you need to know.

Been using PoolMath, it's a great tool.

CYA drops due to splashout, backwashing, overflow, etc. It also drops very slowly just due to being broken down by the chlorine. It can also be broken down by bacteria in a swamp which would show up as high CC levels upon opening. Seems that maybe you should test it more often than every few years

Not a lot of splashout, hardly any overflow, especially this year with drought, and I mostly backwash through a separation tank (or just take out the filter grids and rinse them off.