The Clarisea will only take out debris that is in the system, a bit like a skimmer. It is common for the unit to remove a lot when it is first installed on an established aquarium and then slow down as most of the particles that have been floating around the system are removed. The water level in the body normally runs within 2" of the float switch, depending on the water level in the sump. As long as you can see the water level rising slowly over a few hours and then triggering the float to advance on the roll the unit is working normally. If the water level in the Clarisea is low and not rising to trigger the float then water may be escaping from the unit instead of going through the fleece. In this case check that water is flowing in to the unit correctly and that the bipass on the bottom of the unit is closed. Please note that if the fleece is new or has been wound on manualy it is normal for the water level in the unit to run low, the water level should rise to normal operating height within 5-7 hours.