I'm going to start with soil, then cap it with rocks. I'm going to upgrade my light system to something that will work will with fish as well as boost growth. I'm not sure about a co2 as i've heard their really expensive, especially refills. but additives etc. I wouldn't mind. I'd be keeping my female sorority as well as some other fish in there. Right now I only have 8 females. lol I think they'd love a 55G.