Sand filters catch dead algae better than they do live algae (green = live).

So, kill the algae. With 22K gallons, and 45ppm CYA, you'll need a dose of 20+ ppm chlorine to do so. On your pool, that's 7 gallons of plain 6% bleach. Add it in the evening, then stir up the pool with a brush. Depending on how much sludge you have, you may need to repeat this several times.

If you haven't already, read the Best Guess page, so you understand what's going on. (Link in my signature!)