1. Don't backwash, till the pressure goes up.

2. If the pool is gray/blue with NO green, but still cloudy, it's a filtration problem, not a chlorine or algae problem. (DEAD algae is a filtration problem!)

3. Do go ahead and put 3 - 4 cups of DE in the filter. Do NOT backwash till you see a pressure increase, over the just backwashed pressure. If this does not happen after 2 - 3 days, post that info. (I'd really expect it, after 24 hours).

4. Make SURE the DE is not going back into the pool.

5. If you haven't already, add several gallons of bleach and then carefully brush the pool. There may be unseen pockets of algae that you need to expose and kill.