Why the sponge helps
The porous surface supports biological filtration while preventing tiny fry from being pulled into a narrow intake. Fry may also graze microorganisms from the surface.
Match air and size
Use enough air to move water through the sponge without turning the tank into a current. A large crowded grow-out tank may need more than one filter.
Mature before use
An unused sponge is only foam. Seed it in a healthy established system and verify water quality after transfer.
Clean without sterilizing
Squeeze debris from the sponge in removed aquarium water when flow declines. Alternate cleaning multiple sponges rather than stripping all biological media at once.
Watch for hidden problems
Check airline connections, check valves, air stones and backup power. A silent air pump can mean filtration and oxygenation stopped.