Here's a puzzler from last year, which has reared its ugly head for me upon opening this year.
I have a 20,000 gal in-ground pool.
Hayward S-220T Sand Filter, with Vari-Flo XL valve, all powered by a Hayward Max-Flo 1 HP pump, model SP2807X10.
Last year I was getting progressively more and more sand in backwashes. I removed all the sand to look at the laterals last year, and no cracks or breaks. I NEVER have ANY sand in the pool, which (from reading TFP) would mean a broken lateral.
Today I backwashed on opening and filled a 28 lb kitty litter bucket FULL of sand (after shoveling it from the driveway), from about 30 sec of backwash. I can hear/feel it "blow out" as soon as I start the backwash for the first 2-3 seconds. Solid sand. Then water comes right behind it.
I had problems at the end of last year filtering, not getting the fine stuff (since I'm most likely blowing that out first). I messed around with a sprinkle of DE, but I shouldn't have to. And I shouldn't be losing 30 lbs of sand on every backwash! I've had the house/pool for 3 years, and this did not happen the first year.
Could this be the filter's Vari-Flo valve, or the sand itself?
My local pool store gurus have been no help, they've never heard of this before.
Any help would be very much appreciated!