High CYA - to drain or not to drain

[CourtRob]

I'm back and need some advice. Right before Hurricane Beryl, we drained the pool about halfway (live in Houston, TX) and successfully got the CYA down. We have an 11,000-gallon plaster pool that is 12 years old and are first time pool owners. I'm currently using liquid chlorine, but the CYA went back up due to our former pool company adding tablets after me asking them not to. So we're back up to 100 CYA. The free chlorine is low right now and I was about to add more (don't want to waste if I'm going to drain), but would it be worth it to drain it again and refill, knowing that no tablets will be added to the chlorinator this time? Or 12 years in to our plaster, do you think the plaster is porous and that's the reason we will continue to have high CYA? We aren't experiencing any staining/algae. The pool actually looks great. TFPro test kit results below. ***Something to note that the City of Houston is charging us a flat rate for water usage each month until they get their ish together. So we're charged for using a certain amount and that cost does not increase if we go over the prorated gallon usage.

FC - 3.5
CC - 0
TC - 3.5
CH - 300ppm
TA - 70
CYA - 100

 

[Newdude]

Drain half and refill. Make sure you don't flirt with min FC in the meantime or you might end up fighting half a swamp afterwards.




Did you do a dilution test to confirm the CYA is near 100 ? 90+ is sketchy to read and it may be higher. Mix up a sample of half pool and half tap, proceed with the rest as normal and double the amount.

If it's much higher than 100, you could end up not draining enough and back at square one. The subsequent drain will lose 'new' water with the old, although you're not paying for it. Lol.

 

[Mdragger88]

I say definitely do as Newdude suggested & drain/refill while you’re on flat rate. Those kinds of opportunities don’t come around often!
In hot sunny Houston you may wanna aim for around 60 ppm cya this time of year so not quite 1/2 your volume if you’re indeed currently at 100.

 

[mknauss]

do you think the plaster is porous and that's the reason we will continue to have high CYA?

That is a falsehood. Does not happen.