The best way to thoroughly clean a D.E. filter is to take it apart, remove the grids and clean each one separately to remove oils, dirt, algae and mineral deposits that become embedded in the fabric covering each grid. It's a messy process, so be sure to pick an area with good drainage where water, D.E. and the cleaning agents won't damage your plants.
Taking the Filter Apart
Backwash the filter to remove as much D.E., dirt and debris as possible. After backwashing, leave the filter valve set to backwash and the pump turned off while you are working on the filter. Disable the time clock so the pump doesn't come on while you have the filter broken down.
Open the filter tank and remove the filter grids. On some models, the whole assembly (including the manifold) comes out in one piece. On others, you will have to remove the grids one at a time. Follow the instructions in your owner's manual for your particular model.
Cleaning the Filter Grids
Hose each grid off with a high-pressure, gun-type hose nozzle. Inspect each grid for tears and breaks as you work. Replace any grids with torn fabric or crushed ribs.
Remove embedded oil and lotion residue, dirt and debris by pouring a solution of a safe degreasing agent, such as Simple Green, over the surface of each grid. Let them soak for a few minutes, then hose them off thoroughly. If the grids don't look uniformly clean after this treatment, acid wash them.
Mix a 50-50 solution of muriatic acid in a 5-gallon bucket. Always add acid to water--never water to acid--to prevent a dangerous chemical reaction. Wear rubber gloves and rubber boots to protect yourself from the acid. Don't breathe the fumes. Lay the grids on the ground and pour the solution over them so the acid mixture completely wets each grid. Alternatively, use a 30-gallon plastic trash can. Fill it about 3/4 full with the acid solution and let the grids soak in the solution for a few minutes. Never mix any other chemical with the acid. Neutralize the acid solution with soda ash and dispose of it safely as soon as you finish cleaning the grids.
After soaking, wash the acid mix off and rinse the grids completely. Before putting the grids back in the filter tank, remove any D.E. that may have settled in the tank bottom.
Reassembling the Filter
Inspect the collection tube or manifold O-rings and tank gasket for wear. If they appear to be in good shape, lubricate them with a silicone lubricant. Re-install the grids and tighten any nuts and bolts that hold the assembly together. Close the tank and set the filter valve back to the filter setting. Start the pump, bleed the air out of the tank and add the required amount of D.E. for your your filter.