What happens at night time when there is no water flow?
The filter bed is not suspended when there is no water flow. The filter bed will rest. For top performance it is recommended that the filter media rests 8 hours per day. This is never a problem in a residential installation. In commercial application running 24 hours a day you will need to design and alternate a two filter system that will allow one of the filters to rest while one of the filters is in service.