Lowering CYA, pool draining help needed

[chaserot]

So ... after spending a few hundred $$ at Lesli's and getting Terrible advice on my green pool (hey, lets put lots of conditioner in ...) I now find my pool with a CYA of 140 (tested by Lesli's this am), cloudy, and the need to lower it asap. It's been properly shocked and the color looks good, there is a small amount of FC but lots of TC. After reading a lot of threads on this board I believe that my only solution is to drain 50%+ of the water.

I have a 29k gal fiberglass in ground pool, is there any risk of me draining too much water out at a time? Any risk to harming the pool? It's July here in Norcal I believe the ground water level is lower than 10 ft. I think so that is ...

One possible strategy would be to pull water from the deep end filter (through the Sta-rite tx-135 filter while keeping the skimmer inlet closed), drain it from the hose outlet on the filter - while adding water to the shallow end. Oh, one other question - when the CYA number is lowered, will the bound Chlorine unbind in the remaining water? Now sure how this works chemically.

Just thinking, not sure on the best strategy here. I just ordering the TF-100 test kit to be delivered mid-this week.

Any thoughts here would be great! Thanks!

 

[BadOleRoss]

Odds are you are going to end up draining and refilling more than once. CYA levels over 100 are difficult to get an accurate reading on. As far as water levels and FG pools I will let someone else chime in but you might give your installer a call and see what they say. Once trick that has been used on smaller pools is to cover the pools with a tarp....siphon water from under the tarp as you refill the pool on top of the tarp. The tarp will pretty much stay between the old/new water. When you have replace what you want....remove the tarp. With your pool being 29000 gallon, I doubt you have that big of a tarp.

 

[jblizzle]

There is certainly a risk to draining too much of an inground pool. You have any idea where your ground water table is?

I think you may want to only drain a foot or 2 and then refill and repeat. Or try draining from one end and filling at the other, but that will likely use more water.

Getting the CYA to around 50ppm will serve you well through the rest of the summer.

 

[bmann71]

Even if the water table is low in your area I wouldn't recommend draining much below the skimmer of your pool. You have a greater threat of the sand bed below your fiberglass shifting if you remove to much water and after you refill, it can create pockets underneath thus causing a crack. Trust me I know it happens.
I suggest doing it in small increments. May take more time and water but it's a safer way to go. Cracks in fiberglass can be fixed/patched but they are unsightly and you're better off to just avoid them.