I have a submerged power filter on my bichir tank. The filter puts out a strong current, with the fish don't appreciate. To slow the flow, I put a spraybar on the outflow. Then I slip some filter sponges over the spray bar. I figure bacteria can grow on those sponges, and as a bonus, the sponges slow down the bubbles from the venturi valve the filter has. My thinking is the longer these small bubbles are in the water, the more gas exchange will happen. The scuds and crayfish babies like grazing on the biofilm too....