FC level band at 10ppm - How measure pH?

[goody222]

So I'm keeping the pool open for the winter and my CYA is currently 80ppm (going to let it drift down of course). With the salt cell off for the winter I'm supposed to follow the "Non-SWCG" FC/CYA bands with a target of 9-11ppm for CYA=80. My FC is currently 11.0. I've read that pH is not accurate above a FC of 10ppm (important when SLAMing). Do I just need to let FC drift below 10ppm, then measure pH? Or is 10ppm a conservative number for pH and I don't have to worry about it with a FC = 11? What do you think? THANKS!
-Mark

 

[mknauss]

Your CYA is not likely to 'drift down' over winter, unless you foresee lots of overflow due to rain and snow. It takes very warm water temperatures to have CYA degrade in any meaningful quantities.

Your best bet is to test pH when your FC is 10 ppm or less. Then add your acid (if necessary) and your chlorine to get back to your target range.

 

[duraleigh]

at FC 11 ppm, you can essentially disregard what very small error there will be if any.

 

[goody222]

Thanks, I guess I'll try a little experiment at 11 and below 10 just to see. Interesting also to see what happens to CYA, last year it was zero come spring time. Very little draining last winter also. Thanks!

 

[tomfrh]

It should be ok at 11.

you can also dilute the pool water with tap water or bottled water and measure it.

eg if your tap water is 7.4 and a 50:50 mix of pool and tap water measures 7.5 then your pool water is 7.6

 

[Killer95Stang]

At low enough temperatures, algae pretty much doesn't grow. So I personally do not think you need to revert to Liquid Chlorine numbers in order to keep algae at bay. I'm on my 5th complete season with my pool and I've never adjusted to a higher fc levels during the winter. I have noticed higher than expected levels of fc, due to lower losses of chlorine. When that happens, I just skip a day, but I'm still keeping my chlorine between 5 - 7 ppm. (CYA 70-80)

If I'm off base, then correct me please, because I'm just going off 5 years of observations without ever having an algae bloom.

 

[Saturn94]

If you read your pH level immediately after mixing in the drops (don’t let it sit), you’ll get a good reading. Using this method I’ve been able to get a good reading up to about 14ppm FC.

 

[goody222]

OK, I'll try that. If I have to SLAM next year, I'm going to do my own test as I add Bleach. Thanks.

 

[duraleigh]

Thanks, I guess I'll try a little experiment at 11 and below 10 just to see.

Please do that and report what you find.