hello, my 15 gal: 8 cardinal, 6 rummy, 1 pengiun tetra, 2 blue rams, all those fish arent at full size... is it overstocked? i want to get 2 corys to combat the tank pollution, so would the corys eat wastes from other fish? would they eat their own wastes? so if i get 2 corys for my tank, would it be still overstocked since the corys will eat all the wastes? would it make the tank less overstocked? less waste?