Recently I noticed that the flow light is slow to turn from red to green when the pump turns on. Returns show strong flow and filter pressure is 5psi over initial charge with DE. When the pump turns off the flow light stays green for some time despite no flow. I washed out the cell with a hose and also did a muriatic acid wash this morning hoping this will fix it. Any other recs? We are 1 yr into a 3 yr warranty