Hello Maxime,
My Common Snapper is about 12" shell length, and the tank is a 75 gallon all glass. The filtration is a 300 gph Little Giant submersible pump at the bottom of a kitchen garbage can, water is siphoned over the top of the aquarium using 1 1/2" PVC to form a P-trap to maintain water level in the tank. The water gets pre aerated by going to a Tee that is open on top and has a length of pipe going down to a couple of 90 deg ells to form another trap that cascade into an upper level container that is loaded with air conditioner filters. This is a cross flow set up that after going through the filters, drains through small holes for after aeration, to the sump where the water gets sent back to the opposite end of the aquarium.
