Backwash once a month regardless of pressure. However, if your pressure gauge indicates a high reading, (approximately 10 P.S.I. over your normal reading), backwash immediately. The longer you wait, the harder the dirty DE powder becomes, the more difficult it is to get out of the grids and tank. 

Unroll your blue backwash hose to the area you want the dirty DE powder to go. You will lose about fifty gallons of water to backwash. 

Turn off your pump. 

Turn your multiport valve to the backwash position. Turn on the pump. Watch the blue backwash hose to ensure that it does not kink, or worse, explode! Watch the sight glass on the multiport valve; you will see dirty DE powder running out of the system, after the water has run clear, shut off the pump. 

Turn your multiport valve to the rinse position. Turn on the pump. Rinse the tank for ten seconds. This will dislodge any DE that is stuck in the corners and crannies in your filter tank. Turn off the pump. 

Repeat steps 4 and 5. 

After the final rinse, turn your multiport to the filter position. It's time to replace the DE that you have just backwashed out of your filter. This is added into the closest skimmer to the filter with the pump running. Add 4 1/2 scoops of DE powder to a 36 square foot filter, 5 scoops to a 48 square foot filter, or 6 scoops to a 60 square foot filter. If using a one pound coffee can, add an additional scoop.   

That completes the backwashing procedure. Mark your calendar and be sure to backwash once a month to ensure crystal clear water! 

For sand filters, the procedure is the same, with the exception of the addition of DE to your skimmers!