I'd like to set up a 20g long tank with some vallisneria, river rocks, and sand substrate. I'd like a current, so I'm thinking about using a canister filter with the in flow tube on the opposite end as the out flow tube. I'm also going to take two power heads with an under gravel filter. One with normal flow, and the other with reverse flow on the opposite end of the tank. The idea behind this is to create a cycle effect with water flowing one way above the gravel, and the other direction under the gravel, simulating a river. Since zebra danios love current so much, they will be the centerpiece of the tank. What else could go in there?