My pool has been opened for about 3 weeks this season. The filter was extremely clean at start-up and for the past several weeks the pressure gauge has remained at the initial level from when the pool was opened (the pool has not been used much and the pool has stayed clean with just a few vacuum's). However, yesterday and today, the needle has dipped below the starting point. I have never seen the needle go lower when the filter is running normally- of course it usually rises over time. Is the dip in pressure anything to be concerned about (picture attached)? The filter is functioning normally and the water test results are normal.