I'm trying to get better filtration from my sand filter by adding DE. Pool school says 1-2 cups should typically give me a 1psi pressure rise. It took 5 cups to get that 1psi rise. 300lbs of sand in the filter as per spec. Why is so much DE required with my system? I just rechecked pressure 6hrs after I introduced the DE into the system and it is up an additional 0.5psi which I attribute to contaminants being cleaned out of the water. Water is clear and properly balanced.