I would do a nice center piece of driftwood with some anubias nana or java fern on it. Some kind of carpet plant with contrasting texture like microword if you use anubias or baby tears/hc if you use java fern. You could even use something like cryptocoryne wendtii or lutea as a background in a tank that small.
i have a 5 gallon hex ... this filter is the only one that fits my tank other than a sponge ... and i just bought it i am going to stick with it the current doesnt seem to even bother him he swims fine
40 gallon - Misc fish
15 gallon - Axolotl
5 gallon - Betta and ADF
20 long - Hatchling turtles and corydoras.