A weird thing about CYA

[pikeman]

I had the perfect level of CYA in the pool before I turned the SWG on and it remained stable for over a year. No problems at all. So much so that I neglected checking the CYA for a few months and then it seemed to be zero. None at all! I thought my reagent was no longer any good, and had a sample tested by a trusted capable pool store; it was one of those new-newfangled computerized ones, and that test showed zero! CYA isn't supposed to go away, and I didn't do anything with the chemistry. I happened to have some CYA and put two cups in a cheesecloth bag, suspended it off a board in the deep end and it dissolved after about three days. My test kit still showed zero, and suddenly my SWG was indicating low salt. My tester showed about 4000PPM, so I inspected the cell and it was all clogged up with white stuff. I'm assuming it was the CYA. I cleaned it with acid and everything seemed OK. I have had there were no problems keeping the pool at 3-4PPM FCL despite the lack of CYA and lots of sun. The SWG was running for six hours at 70% and it's rated for twice the capacity of my pool.
So I'm really puzzled about the disappearing CYA, and also wonder how it can be added without clogging up the SWG again.

 

[Texas Splash]

I see a couple issues with your situation. First, it's important to remember that CYA does degrade and disappear over time, but it's quite slow. Maybe 5 ppm per month or so. Just depends on the pool, amount of activity, etc. The other time CYA can seem to drop "unexpectedly" is if there's a leak. That brings into consideration the salt level issue because a leak would also explain where the salt went. The white stuff you saw on the salt cells was more than likely calcium and not stabilizer.

Does your pool have an auto-fill? Have you noticed an increased amount of top-offs in the past few months? Also, if your pool CYA was extremely low, then 2 cups in a 20K pool wouldn't do much to increase it anyways. You need to add more like 8.5 pounds just to get to a CYA of 50.

 

[Rattus Suffocatus]

If you have an autofill then... yeah.. turn it off for a week or so... that would rule out a leak. But that is a very good reason to test CYA at least every couple of weeks. I've been lax at that since it didn't change at all in the first month or so. Good to know, honestly.

 

[YippeeSkippy]

I'd say its fine to test CYA monthly to Bimonthly as long as everything is running well otherwise.

Autofills do certainly have a way of hiding leaks, but sometimes after horrendous storms where you later drain some from the pool (common in FL, for example) you are also draining out some chemicals there too.

Maddie

 

[pikeman]

I see a couple issues with your situation. First, it's important to remember that CYA does degrade and disappear over time, but it's quite slow. Maybe 5 ppm per month or so. Just depends on the pool, amount of activity, etc. The other time CYA can seem to drop "unexpectedly" is if there's a leak. That brings into consideration the salt level issue because a leak would also explain where the salt went. The white stuff you saw on the salt cells was more than likely calcium and not stabilizer.

Does your pool have an auto-fill? Have you noticed an increased amount of top-offs in the past few months? Also, if your pool CYA was extremely low, then 2 cups in a 20K pool wouldn't do much to increase it anyways. You need to add more like 8.5 pounds just to get to a CYA of 50.

Thanks for the input. I recently had a fresh finish coat installed and the lines were static tested. I do have an auto fill, but also watch my water use pretty carefully. Based on the replies I’ve received I think the deterioration of the CYA is the most likely cause. With the SWG removed now for the winter I’ll be using some tricolor pucks and that’s going to build the CYA up. I’ll just have to keep an eye on it until Feb or March and switch to bleach if it gets too high.

 

[pikeman]

I'd say its fine to test CYA monthly to Bimonthly as long as everything is running well otherwise.

Autofills do certainly have a way of hiding leaks, but sometimes after horrendous storms where you later drain some from the pool (common in FL, for example) you are also draining out some chemicals there too.

Maddie

Good point about the rain. We did have some very heavy storms and the pool level went over the standpipe that’s part of the auto fill. I needed to add some salt to get back to the optimum level. So the CYA may have washed out.