Closing with High CYA

[autoxer]

First, a little background:
I'm in my 2nd full season of owning a pool, and, until very recently, was not using BBB. To maintain a clear/clean pool, I was using pucks for chlorine, MA for lowering ph (never needed to raise), and Sodium Hydrogen Carbonate to increase TA (never needed to lower) and Powder Shock "Plus" (sodium dichloro-s-triazinetrione; supposedly shock+clarify+enhances filtration (whatever that means)+no ph increase).

Also, our pool came with a Frog mineral system which we've used , but :!:, per builder recommendations, we only used the mineral pack, not the "bac-pac" (copper) or chlorine dispenser (whatever they call it). I know there are a lot of Frog haters here, but so far this has worked well for us, and "allowed" lower FC levels without problem (or we got lucky, so far anyway). Makes sense as essentially it's adding silver which is known to be effective. With this method, we've maintained FC at 1-4 with no algae and clear water. I do plan to drop use of the Frog next season however, as now I'm becoming TFP educated Besides, those mineral packs aren't cheap, nor easy to find.

So, my problem is CYA... I'm not quite sure why, but as the weather turned cold here my CYA levels shot up the last few weeks. I know they were already up (I now know because of the pucks) but it had been in the 60-80 range for several months. Now it's ~120. I don't really see the point in draining/replacing water to lower it when I'm about to lower it to close and fill with rain/snow over winter and top off in spring to open.

I'd like to close my pool this weekend, so I'd like to go ahead and shock. My concern is according to the tables I need to raise FC absurdly high (e.g. 40+). At those levels will it drop to an acceptable range anytime soon (e.g. this weekend) and/or does it matter if FC is sky high when you close it up. Since I'm still under the effects of the Frog, do I really need to raise it that high?? Am I better off wasting a lot of water draining / replacing it to lower CYA first?? Other ideas??

Note that I have a dark plaster bottom which we don't want to "bleach" as well, which leads me to a followup question - can I put that much bleach in w/o staining/lightening the plaster (pool calc says ~13-14 gallons!). Over two years, we can actually already note a "fan" like area in front of the returns where the plaster is slightly lighter, and although I can't say specifically what caused it, I would assume chlorine.

CH: 280
FC: 1.5
TA: 110
CYA: 120 (est. - out of range)
~54 deg.
CSI = .02

Thanks for any advice!

 

[polyvue]

So, my problem is CYA... I'm not quite sure why, but as the weather turned cold here my CYA levels shot up the last few weeks. I know they were already up (I now know because of the pucks) but it had been in the 60-80 range for several months. Now it's ~120. I don't really see the point in draining/replacing water to lower it when I'm about to lower it to close and fill with rain/snow over winter and top off in spring to open.

I'd like to close my pool this weekend, so I'd like to go ahead and shock. My concern is according to the tables I need to raise FC absurdly high (e.g. 40+). At those levels will it drop to an acceptable range anytime soon (e.g. this weekend) and/or does it matter if FC is sky high when you close it up. Since I'm still under the effects of the Frog, do I really need to raise it that high?? Am I better off wasting a lot of water draining / replacing it to lower CYA first?? Other ideas??

Well, you know the drill... so don't shoot the messenger!

Others will surely be along to provide details or more nuanced advice but your best bet under the circumstances is to do what you'd rather not do: drain half of the pool water so you can get the CYA down to a more manageable level. This will enable you to shock with half of the chlorine and give you, if nothing else, some peace of mind this winter.

 

[taekwondodo]

My rec is slightly different: wait until spring before you measure your CYA.

For example, a friend of mine has a pool that measured ~100+ CYA in July. We've had quite the storm last week and he asked me to come by and check on his pool. For grins, I wanted to see the new CYA measurement: 60-70ppm. You're on the east coast and you'll get quite some rain over the winter... And, since you're in the cooler months, algae growth darn near stops - and Cl usage is minimal.

Once things start warming up, see what the dilution of the CYA was over the winter, and start anew. Otherwise, you may get it perfect now, and have to re-adjust (add CYA) in the spring.

- Jeff

 

[frustratedpoolmom]

Yes, it's safe to use that much chlorine, use clorox or pool store 12.5% and make sure you leave the pump running during the shock process. Shock, make sure it's holding, then do your winterization. In the spring, refill, recirculate, retest and then see where you are at CYA wise, you can always do an additional partial drain at that time.

You won't regret ditching ole' froggy. Your wallet will thank you.

 

[PaulR]

I agree with taekwondodo, wait on fixing the CYA until spring.

When you add the bleach, pour it slowly in front of a return jet with the pump running, so it disperses quickly. That will minimize the risk of bleaching the liner.
--paulr

 

[duraleigh]

CYA acts as a "buffering agent" (in a sense) so your FC is not nearly as powerful as you might expect.

Chem geek has a post on this on this forum but it's basically that 3-4ppmFC with no CYA is somewhat equivalent to 30-40 FC with 100 CYA.....in other words, with that much CYA do not worry about overdosing with FC.

I would shock, drain the pool to closing levels and fix your CYA in the Spring......it's probably not the textbook method to cure the issue but it will suffice and it will be easy on the pool boy (you!). You will likely find your CYA has come down to a more manageable level anyway.

FWIW, anytime someone records a sudden jump in a parameter when they have done nothing to change that parameter, a testing error comes immediately to mind. You should double check your testing method and then proceed if you are comfortable with the result.

 

[autoxer]

Just a quick update on this one...

It actually warmed up here for a bit so we didn't close a couple weeks ago when I originally planned. I did re-run the test, and still finding CYA to be excessively high. I was a bit surprised with the most recent tests, but it isn't like it was overnight, just faster than I would have expected. Now I know not to use tablets...

In hindsight, in case anyone finds themselves in this position in the future, I really think I should have at least tried to bring the CYA down some through water replacement, even if not all the way to a decent target like 40... At 110-120, and trying for a TC of 42+, well, that's just a ton of bleach... I used something like 16-18 of the big jugs to shock before closing, and at those levels you can smell the chlorine 20' from the pool. If I had to do it over, I think I'd try to get it down to 70 or so for closing and then see if winter corrects the rest with snow/rain and fix any remainder when I open.

 

[PoolGuyNJ]

Let me add that using dichlor as a shock will also raise the CYA. I only use dichlor when there is no free CL in the pool and it needs it now. I prefer to see people use sodium hypoclorite (bleach or 12 %) or cal-hypo.

Scott
PoolGuyNJ