24' round pool, 4' height 12" dug out center, I figure ~17,000 gallon pool.

Based on $15 test stips from walmart

CYA 30-50
Hardness 200
Alkalinity 80
PH 7.6-7.8
Chlorine 10+

Pool was first setup in July and I went fine until about a week ago I noticed algae in the pool, presumably because I had let chlorine get too low.

I added a bottle of algaecide stuff that came with my pool, but don't think I'll bother adding more.

I have the 250 lb 1/2 HP sand filter running now 24/7.

At first I raised chlorine with one bottle bleach and 2 of the shock treatment bags from walmart (~50% calcium hypochlorite). This did lower the algae levels and 2 days later looked better, but not resolved.

I went to pool store and was told to add 7 bags of their powder plus after scrubbing again. This stuff is about 75% calcium hypochlorite, so 7 bags raised chlorine levels high.

Yesterday the pool looked good: wasn't cloudy, no chlorine. This morning I see algae creeping in again, it's at the bottom about 1-2 feet in, generally setting in the low spots in the sand.

I REALLY thought I'd hit that critical point with my initial chlorine level, but if I did the algae has magically reappeared

This is going to get expensive fast. Thanks for any help!