When the pressure is too low on the gauge, or better yet, when you can stop the flow of water from the jet when you put your hand over it.

N.B: Each time you change the position of the handle on the filter head, it's better to stop the pump and start it again.

Place the filter handle to "BACKWASH" for about 2 minutes, then on "RINSE" for about 1 minute, then to "WHIRLPOOL" or "RECIRCULATE" for 15 minutes, then back to "FILTER".