I was going by the idea that you add DE until you get a 1 psi jump in the pump pressure. That's the way that I understood it from reading the forum. I went until it jumped 1 1/2 psi. So, If I added to much, how does the DE get into the pool? I thought it would have to go through the sand first. When Poconos mentioned "blow by" is there some sort of relief built into the filter so that something blows by the sand before the filter is damaged? I mean we're talking about 15 psi, I can create more than that putting my thumb over the end of a water hose.