Back the beginning of May we had replaced the Silica Sand in the Pool Filter drum.. The Pool Store advised filling the drum back up with only 3 bags S/S as to fill it up to the 4 bag capacity we'd be wasting quit a bit... And that is where we are now... When we go through the ritual of vacuuming the pool we must be doing something wrong... When I shut off the pump to clean out the basket on the pump I turn the value closed leading from the Skimmer and I turn the dial on top of the Drum from Filter to Backwash to release the pressure as I'm removing the cap to the filter basket.. ( power to the pump is turned off )... Before turning the Power to the Pump back on I open the dial back to filter and open the value... It's at this point we notice a considerable amount of Silica Sand has come out through the Return to the Pool and settled on the bottom... What am I doing wrong, any idea? Thanks..