Where did my CYA go?

[mjnorman]

Hi all. Long time reader here, have been using the tfp method for a couple of years. First a little background. We had our pool opened this year, brand new liner installed. Pool looking great. When the liner was installed I installed an SWG, a Hayward aquatrol-rj. I was running CYA of 80, and FC holding fine.

Flash forward, we had a house fire and have been displaced for going on 3 months. We went about 2 months before getting power turned back on at the house, and of course the pool being about the least important thing to worry about, it turned to a green pond as you would expect.

So I've been slamming, going well but notice I'm burning through chlorine like crazy. I'm at the point where my algae is mostly dead I think, I was finally able to see the bottom today.

Anyway since I knew what my CYA was and CYA never goes away (right???) I have been using 80 on the calc. I checked it today for the heck of it and it registers ZERO CYA. I've done the test twice and this is with a brand new Taylor tf-100. How is this possible?

 

[jblizzle]

There's a bacteria that can convert cya into ammonia so it would all disappear. It would also result in you consuming a lot of chlorine to get rid of the ammonia before you can start killing the algae. When you were testing your FC where you also testing the CC at the beginning it very likely could have been very high.

 

[mknauss]

It is possible, under certain conditions, especially when left with a severe swampy algae outbreak, for a bacteria to attach the CYA and consume it. That creates ammonia. The ammonia takes a tremendous amount of chlorine to clear.

Sounds like you may have already gotten there as you state the algae is dead.

If the pool is now holding FC for at least 15 minutes (test it, add enough chlorine to get to 10 ppm, circulate, and then test FC in 15 minutes, you need to have 7 or above remaining), you can add 30 ppm of CYA and finish your SLAM Process

Good luck

 

[mjnorman]

Well shoot. No I did not check CC I didn't think it really mattered since it was green. I had no idea it was possible to lose CYA. Should I check anything else before dumping stabilizer to get back up to 80?

 

[mknauss]

I would suggest doing the test I outlined in my post above.

- - - Updated - - -

And do not take the CYA back to 80. Go to 30 ppm CYA and then complete a SLAM Process. Once you pass the three criteria, then raise your CYA for your SWCG.

 

[mjnorman]

Yep we cross posted. Thanks so much for the feedback. It is definitely holding FC but I will confirm and follow your suggestions. At least insurance is paying for all the chlorine I've fed to the nice and hot Tennessee sun haha.

Thanks!