CYA and pool draining

wkduffy

New member
May 21, 2019
2
Florida
Hi friendly, informative pool people! Newbie here going through my first CYA battle...and the CYA is winning. Initially my readings were 100+ (so who knows exactly what the ppm was). So, I drained about 13 inches down about 6 times now over the last 3 days; I've heard too many fiberglass shell horror stories about draining too much, and I am proceeding with an abundance of caution. And as you've probably already guessed, testing after each refill has shown me next to no results. Actually, the CYA level has seemed to drop a tiny bit (or it might be wishful thinking on my part as I stare at the black dot), so I did the half-pool and half-tap test. The CYA seems to come up as 70 at this point, meaning I am likely still somewhere around 140 ppm.

Question: Before I do another 13-inch drain and refill dance while burning through another bottle of reagent, is there someone here who would boldly tell me to "get on with it" and just drain half my pool? I've read about hydrostatic pressure, and ground water, and mythic tales of pools buckling and rising out of the ground. I am in Highlands County Florida, almost pure sand soil, and as the name suggests, I live on some of the highest land in the state--it's all relative of course. We built the concrete deck ourselves, and when the county inspector came, his eyebrows went high in the air when he saw how much rebar we used to tie the pool in--he said "Wow, that pool ain't going nowhere!" I don't know what the groundwater situation is, and there is no sump in the ground. We never have standing water, even after a hard rain, there was no water in the hole when the pool was dug. The pool is a fiberglass shell, 13k gallons, 2 years old. We just converted to SWG after having used tons of chlorine pucks and stabilizer over the first 2 years...our culprit.

How safe is safe when it comes to draining and trying to correct this CYA problem? I know no one can guarantee anything, but am I being overly cautious here and just wasting time and water? Or should I just continue the 13-inch draining dance forever until results appear? Any advice welcome.
 

mknauss

Mod Squad
TFP Expert
May 3, 2014
17,896
Laughlin, NV
Welcome to the forum!
You can exchange some water without draining.

If you place a low volume sub pump in the deep end and pull water from there while adding water in the shallow end (through a skimmer or into a bucket on a step so you lessen the water disturbance) you can do a fairly efficient exchange. That is assuming the water you are filling with is the same temperature or warmer than your pool water. If your fill water is much cooler than your pool water, then switch it. Add the water to the deep end (hose on bottom) and pull water from the top step.

The location of the pump and fill hose may change if you have salt water, high calcium, etc.
In my pool, with saltwater and high calcium when I drain, I put the pump in the deep end and hose in shallow end. The water in the pool weighs more per unit volume than the fill water from the hose.

Be sure to balance the water out and water in so the pool level stays the same. Also be sure your pool pump is disabled during this process. Once started do not stop until you have exchanged the amount of water you wish.

I suggest you read ABC's of Pool Water Chemistry and consider reviewing the entire Pool School eBook.
 

wkduffy

New member
May 21, 2019
2
Florida
mknauss: Brilliant! I did a lot of reading looking for the answer to the draining question and never did I see anyone suggesting a water exchange. I did this exactly as you suggested, and it was so effective that the CYA went all the way down to 45 in a few hours time. Since we have a newly installed SWG, I guess I need to get it back up to 80. But at least now I can control it. Now I'm off to attend Pool School to get my water truly balanced before we install the Pentair Intellichem which came in the mail today--this thing has another novel-sized manual to read. Thanks again!
 
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