Winter Chlorine Level?

Pool company closed pool except for closing my electric cover which I'll do. They put in 5 gal of 12.5% Sod Hypo. I already had a FC of close to 20. CYA roughly 120. What level should I be at before I go ahead and close the cover for the winter? I'm estimating FC of around 32 right now.

I know all these numbers are high overall and will resolve on opening in the spring. The cover will also be replaced in the spring. In the meantime what is the highest safe FC level for winter closing? Thoughts? Everything else is balanced.

Brian.

I'll let those who close their pools advise you on that one, but personally I think that if there were any damage that would be done to your liner, it has already been done. And the higher FC level you close with, the longer it will be before the Cl gets down low enough to let algae grow. I think you would be fine to leave it where it is, but again, I don't close my pool or use a cover--so hopefully one of those who does close pools give you a more informed answer.

Janet

5 gallons of 12.5% chlorinating liquid in 25,000 gallons would increase FC by 25 ppm so you'd be at 45 ppm if you started with 20 ppm. It will drop so it's quite possible you are at where you estimate.

With the 120 ppm CYA in the water, even 45 ppm would be equivalent to around 0.6 ppm FC with no CYA at 7.5 pH so isn't so terrible. On the other hand, the pH probably went up to around 8.7 so would further reduce the active chlorine level somewhat (though not that much).

I agree with Janet that whatever damage was done to your liner (if any) was probably when they poured the chlorine in initially, especially if they didn't do so slowly over a return flow and mix it thoroughly. As the water temps cool, the chlorine will drop much more slowly. As long as it stays above around 9 ppm, you should be fine as far as algae prevention is concerned. If you open in spring before the water warms up, I'll bet the water is clear upon opening.

Richard

I hope it was an old liner! Otherwise it may be a few shades lighter in the spring. Personally, that's why I don't bother with pool companies. As for the closing, unless they hauled away all your stuff, and put on the cover, why pay THEM to dump in the wrong amounts of chemicals?

If you MUST drop you FC levels, there are things you can do, but you should be OK as is.

Your FC really shouldn't be higher than 25-30 and you didn't say what pH is (Higher pH inhibits chlorine's action). But Chem_Geek is almost certainly correct that your pH went up.

For now, don't worry. Water temps below 60 inhibit algae growth, the chlorine will dissipate over the winter and your CYA may well drop to more reasonable levels.

Next season, look at our fall closing threads and save yourself a bundle, not to mention heartache.