Last year I was able to add a cup of DE to my Hayward sand filter to get better filtering. This year, when I add the same amount of DE, the pressure goes up about 0.5psi every 45 minutes. The VERY strange thing is when I shut off the pump, but the filter on backwash (but not turning on the pump), then put it back to filter, and turn the pump back on, the pressure drops to about normal clean pressure. I will have to backwash the filter to remove the DE because I don't want to have a situation where the pressure is rising for "no good reason." I originally thought the pressure rise was due to the increased filtering, but I guess not, since pressure returned to just about normal without backwashing. I can repeat this cycle.
Any explanation on why this is happening in the filter ?