We have a salt pool with auopilot. Can't get the water clear; clearly the filter/chlorinator is not doing its job. The chemicals seem to be ok (I have added shock to make sure chlorine stays good). I keep on seeing the blinking red light and the message :"Purifier off; check flow". I clean the screen, put it back, and a few minutes later I have to repeat. I cleaned the basket. What else could it be?