New Pool with Very High CYA

[strongcedar]

I just moved into a house with a 17,500 gal IG plaster pool. First time pool owner. It's in good condition, and I'm getting closer on the water chemistry. For the first two weeks I was targeting (and getting) 4-5 FC. But I just tested CYA with the TFP test kit (and took water to the local pool store to double check my test), and CYA is between 120 and 150. The BBB FC/CYA chart only goes to CYA of 100, with a target FC of 12. Chem Geek's post goes to CYA of 120, with a target FC of 13.6. I'm having moderate problems with Mustard Algae; meaning I'm scrubbing and brushing just about every time I'm in the pool, obviously because FC has been too low. And Chem Geek's chart targets 17+ FC to combat algae at high CYA.

Here's the question - it doesn't seem particularly safe/comfortable to swim in water with FC of 17+. Any opinions on keeping FC that high permanently? Bottom line is that it seems I'll need to drain and refill to fix the CYA problem.

 

[duraleigh]

Here's the question - it doesn't seem particularly safe/comfortable to swim in water with FC of 17+. Any opinions on keeping FC that high permanently? Bottom line is that it seems I'll need to drain and refill to fix the CYA problem.

The only permanent solution is a partial drain/refill as you suspect. Go ahead and bite the bullet unless your swim season is about to close......if so, the CYA may dilute a lot over the winter.

It is perfectly safe to swim in it because the high CYA makes the effective chlorine much lower than the 17ppm that may be there. Nevertheless, running high CYA and subsequent high chlorine makes the pool very difficult to manage. Your beswt bet is to get your CYA down around 50.

 

[Bama Rambler]

With CYA that high, your best bet is to drain as much water as you can and refilling. The final number needs to be in the neighborhood of 2/3rds reduction. Be particularly aware of your water table, you don't want your pool poping out of the ground. You can do the drain/refill in increments but remember that you'll have to drain a total of more that 2/3rds of the total gallons to get a 2/3rd reduction in CYA doing it that way.

Dave and I were typing at the same time.

 

[strongcedar]

Thanks for the feedback - as I suspected.

 

[strongcedar]

Just a quick "learn from my mistake" update: I did drain the pool to rid myself of the CYA. Took the time to acid wash, fix light, hit stains, etc. Started the refill of the 17K gals 2pm on Saturday. By Sunday morning we were within 8 inches. I turned the flow down and we went to church, visited a friend, went to lunch and back by 2pm.

The pool was 2/3 empty!

Here's the lesson: when you drain a pool using the backwash setting, don't forget to reset the pump to "filter", or your timer will kick on like usual and drain your hard work away!

 

[crewchief47]

Just a quick "learn from my mistake" update: I did drain the pool to rid myself of the CYA. Took the time to acid wash, fix light, hit stains, etc. Started the refill of the 17K gals 2pm on Saturday. By Sunday morning we were within 8 inches. I turned the flow down and we went to church, visited a friend, went to lunch and back by 2pm.

The pool was 2/3 empty!

Here's the lesson: when you drain a pool using the backwash setting, don't forget to reset the pump to "filter", or your timer will kick on like usual and drain your hard work away!

Homer says it best: (that really sucks though )