First I want to say this might sound pretty minor but I monitor my pool and equipment pretty closely so I thought I would put this issue out there to hear any possible problems. My normal Haywood sand filter stays pretty constant at 18 psi. When it gets to 22 I usually do a short backwash and it drops back to 18. I think I only had to backwash last summer only 3-4 times. Last week with my water temperature at around 45 and my pump running 8-12 hours at night to prevent any possible freeze the pressure went up to 22. Since we had a lot of rain that week the water level needed lowered anyway so I backwashed it for about 20 minutes. The pressure only went down to 20. A couple days later we received another 2-3" of rain and I repeated the above process hoping to completely flush out the sand and return the pressure to 18. Started at 20 and ended at 20. Does this increase in normal pressure indicate any possible problems?