I think what you're looking for is my brackish tank. The way that I got it setup now, I got 3 sharks, 6 sailfin mollies, 1 red claw crab, 2 bamboo shrimp and 2 mystery snails. All that in a 55g. Ends up weighing around 1/4 ton (depending on density of water and such). U can put that just about anywhere. The catfish are bottom dwellers, the mollies are midrange dwellers. The crab can't catch any fish to hurt them and eats mostly algae and scraps. The shrimp bother noone and noone bothers them. Neon tetras won't do well with sharks I think. Sharks would get large enough to eat them. Best to buy the largest fish you're gonna end up putting in there and then buying friends that won't eat him or get eaten.