Cool crayfish maybe you should just leave him in there! As for the fluval 13w light, it's rally not too much light IME, although it certainly could warrant co2 or at least excel. A better idea to reduce the flow would be to put a small hole in the tube leading from the pump to the outflow piece, right near the top, maybe 3/16", not bigger. The other benefit of doing it that way is that you can put your heater back there if you do. Otherwise if you put the heater there it won't work correctly because it heats up that small space quickly and then shuts off right away leaving the rest of the tank cold. Another thing about specs.... They all leak eventually alt least a little bit
so next time you redo the tank I'd re silicone it. Also the foam filter doesn't work as well as plain old filter floss jammed in the back compartment, I use accrurel brand floss with great results. What ever happened to the plant growing out of the driftwood?