20,000 Gallon FiberGlass Pool

I have a 20,000 fiber glass pool and need to drain it half way or all the way, when I tested the Cyanuric Acid levels it was around 140. I had to add 6 packs of shock just to keep it blue every other week. Now I am trying to drain it and was wondering once I add the new water which is added from the same hose I use to water the trees, how much Cyan-uric Acid should I add to the skimmer? They have pumps at Home Depot which I will use, but how would it work? Because once I drop it in and plug it in to the outlet isn't dangerous?

Location is Southern California.

Do NOT totally drain your pool or it may pop out of the ground. You can probably safely drain 1/2 to 2/3 but leave at least a foot of water in the pool. After you refill, test your CYA and see where it is before deciding to add anymore. Most likely, your CYA level will be good without any additions.

What kind of packs of "shock" are you using? Is the ingredient dichlor? If so, don't use that any more as it has CYA in it and will take your CYA level right back up where you are now! Just stick with plain household bleach for your chlorine.

Do you have a floor drain? If not, you can use a submersible pump to pump water out. (Use your pool pump set to waste to pump until the water level gets below the skimmer.)

Drain some, test and post current numbers and someone can help you.

By the way -- You'll need a good test kit if you don't already have one. The one we recommend is the Taylor K-2006 or 2006C (same kit, larger bottle of some reagents). If you buy it through the Amazon link in my signature, the Pool Forum makes a little money on the sale which helps us keep this form online. Only buy if the seller is Amato Industries, however. Some other sellers are substituting the K-2005 which you do NOT want.

Hope this helps. Welcome to the forum!

I would not drain a fiberglass pool more than about a foot below the skimmer without reinforcing it so it does not warp. My suggestion would be to do a series of partial drains and refills, each time a foot below the skimmer and allowing the pool to circulate for 24 hours after each fill and then testing the CYA until it is where you want it. If you want to do it all in one shot I would contact the builder or an experienced fiberglass installer to properly reinforce the shell before draining.

Thanks, Evan for that info. Appreciate you chiming in on this one.