I just went out to vacuum again, here's a question regarding the pressure. When I just run the filter, the preasure shows around 17. When I hook up the vacuum, it starts at about 14, then after I sweep a while, it gets up to around 20 before I backwash. I can tell this point because it quits pushing much water out of the return. Should I stop and backwash before it gets to this point, or will it hurt if I continue sweeping at 20 or is there any certain number I need to be aware of to not let it get above?