Fluval filters have four sizes to handle all tank requirements from the smallest to the largest commercial tanks available. Flow rates vary from 103 to 317 U.S. gallons per hour (390 to 1200 Litres per hour) depending on the model. An important factor in the choice of any filter is actual flow rate. The graph shows the flow rates of the Fluval pumps at different heights. The flow rates, when the filters are installed, are installed, are also influenced by exhaust stems, valves, pipes, elbows and filter media.

Fluval return consists of flexible and rigid tubes to allow the return to be placed anywhere in an aquarium. Strong suction cups are provided to assure output tubes remain in position. The rigid spray bar can be used to spray water rather than a single stream. It is desirable to translate return flow into surface agitation with the spray bar. It is very important for oxygen to enter the water, and for excess carbon dioxide to be released to the atmosphere. This exchange can occur only at the surface. The more agitation, the more water molecules are brought to the surface to release carbon dioxide and accept oxygen.