My cartridge filter, with clean or new cartridges runs with a psi of 26. A few weeks ago the pressure changed over night (the pump is off at night) to 22 and the water flow over the waterfall spill way and in the pressure side cleaners was really fast. Then a few days later the pressure changed overnight again to 28 and the spill way was less robust and the cleaner ran a little slower. This has happened a couple of times over the past couple of months and today the pressure is back to 22. What could be causing these big swings in pressure? Thanks!