By far the most common complaint I hear regarding sand swimming pool filter problems is "debris is blowing back in when I vacuum"
1)The first thing to check is the backwash valve,in particular the gasket and/or spring mechanism may be letting debris get past and flowing right back into pool....also,do you have valve in "recirculate" position?..this by-passes filter. Before changing the gasket,try moving the valve around a few times this may dislodge any debris under gasket - of course the pump should be off any time the valve is moved!
2)IF the laterals have holes or cracks,sand and debris may pass through
3)If its new sand,perhaps too much sand was added?...the level of sand should go to the widest part of tank.
4)After back washing,do you put valve to rinse before going back to filter?
5)If the sand is old,it may be time to change sand..if you are going to change sand,do yourself a favor and get a good quality media NOT silica sand..there are links at the bottom of the page below:
Debris or D.E. powder coming out of your swimming pool filter is the most common D.E. filter problem.
1)As above,the backwash valve is on of the first things to check -it may be gaskets or o-rings in a push-pull valve,or a spider gasket/spring assembly in a multi-port valve like a sand filter has,or backwash valve seals built into the bottom of filter.
2)The grids-are they in the manifold securely? Are there holes in the grids? Are some grid frames bent,not allowing nipple to be tight in manifold?
3)The manifold assembly-is the top and/or bottom manifold secure? Does the manifold have crack or holes and what about the manifold's bleed air assembly-are there holes there? How about the pipe that the manifold sits on...is the o-ring missing or defective?
B)On Pentair 2000 series filters there is a hole in bottom manifold for an aerator tube that goes to top holding wheel...many times this tube gets lost/disconnected and lets D.E. back into pool...plugging it up with a stainless steel bolt is the easiest fix.
4)Perhaps an air leak is pushing the D.E. backwards out the
skimmer after the pump shuts off?.....or,it may go from the skimmer out
the main drain on bottom of pool?