AFter you test it to make sure that the DE won't blow through the returns, check your filter pressure. The other 3 mods, and some of the long-time members, add enough DE to their skimmers to make the pressure rise by 1 psi (if you get too high a rise, just backwash it out and try again--note it may take up to 20-30 minutes to see the rise, so don't get in a hurry). The DE coats the sand, making it "dirty", and it helps filter smaller particles that way.