I cleaned my cartridges about a month ago, right after we moved into the house. The pressure once I reinstalled everything was about 17-psi which was higher than I expected it to be after cleaning them. Over the past 4 weeks the pressure on the gauge has been slowly dropping. Last night it was hovering right around 15-psi. I'm not sure if I should pull everything apart and see if the filters are still clean or if they are dirty. Water is still very clean and flow at the returns is good. I haven't noticed a decrease in flow coming from the returns since cleaning the filters or anything like that. Any thoughts?