Probably Need a New Pump

[mas985]

One of the issues with sand filters is that they usually have a hard time filtering out dead algae because it is smaller than 20 microns (filter capability). One way to help the filter is to add a cup or two of DE. This will help remove the dead algae much more effectively.

[FormerBromineUser]

I ALWAYS add DE to my sand filter after backwashing. It is one of the greatest advantages to having a sand filter IMHO. Here's how: (copied from a longer post)

1) Backwash your filter. Note the pressure it's running with.
2) mix about 1/3 of a cup of DE into a few gallons of pool water.
3) pour the mix slowly into your skimmer while the pump is running. If it's a 2-speed, use low speed.
4) WAIT about 20 minutes and see if the pressure rises. If it does you want it to rise about 1 lb.
5) If the pressure doesn't rise, or rises less than 1 lb, repeat steps 2), 3) and 4).
6) If the pressure has risen 1 lb, you are done. (frankly if it goes up 2 lbs, I'm OK with that. ) A 1 lb rise is your target.
7) If it goes up 5 lbs or more, backwash and start again, but use less DE.