How much to drain for high CYA

[M&M Blackjack]

Hello, we moved into our house 6 weeks ago & we are new to pools. We have a SWG but the previous owner constantly had pucks in the skimmers which I know now from this forum is what likely caused our high CYA (and in turn our non existent chlorine) We have an in ground, plaster pool approx 20,000 - 25,000 gallons.

Our water has been looking great, but 2 days ago it started getting cloudy & now has a slight tinge of green.

Our numbers tested today with Taylor test kit were:

FC 0 literally no color at all to the water sample
CC 0
Ph - 7.6
Alk - 90
CYA - best I can guess with a 3 part dilution is around 285 . When I diluted 1/2 the black dot disappeared still before the 100 mark, so diluted to 3/4 and got to around 95. Maybe I didn't do right?

Realizing even if it’s plus or minus a little for human error it’s obvious, our CYA is extremely high & we must drain/refill but how do we figure out how much to drain?

Also, how does one “drain” the pool? When we backwash (Hayward sand filter) I assume it’s coming from the skimmers, so once we get passed the skimmers, then what? Or is there a way to drain from the bottom of the pool?

Can this be done a little at a time or should it be done all at once? Draining & refilling seems like such a daunting task, but if it has to be done we certainly want to do it right & have it be effective.

Please be kind, we are new & determined to maintain ourselves but seeing as we are only weeks from swim time, we are getting a little nervous we won’t get this right!

Thanks for any insight!

 

[Newdude]

Hey M&M and Welcome !!!!

but how do we figure out how much to drain?

An even proportion or %. Half lowers CYA by half, 90% by 90%, etc.

Unfortunately looking near 300, you'll want to drain or exchange 80% or more of the water to end up at 60 or less. Always go more than you think because if you have to drain multiple times, you'll be draining new water with the old.

Is ground water a concern ? The pool may become a boat and float up out the ground if the water table is above the level you need to drain. You can always dig a test hole nearby to be sure. Check this link for the no drain exchange if that sounds better.

Draining - Further Reading

www.troublefreepool.com

so once we get passed the skimmers, then what? Or is there a way to drain from the bottom of the pool?

You want a submersible pump that you drop in. With the bulk of 25k gallons needing to come out, either buy a powerful Submersible pump and a 1.5 inch hose for faster draining or rent a large trash pump from Home Depot or such that comes with the hoses.