Besides me always doing my planted tanks, I do like setting up some non planted tanks. I have 20 gallon tall that I want to stock with probably just one aggressive species since I find the aggressive fish interesting. I am even fine with just one or two fish in the tank as long as they are interesting. So far I was thinking maybe a pair of Figure 8 puffers or a one Green spotted puffer, or maybe a single pair of convicts. I need some ideas similar to this. I don't mind doing freshwater or brackish, I just want an interesting species with some aggression. Any good ideas? I thought the GSP sounds the coolest so far but who knows what other ideas are out there.