This is the first time in probably most of my life that I don't have multiple tanks set up. I only have three one-gallon glass betta habitats. Yes, bettas CAN be aggressive, but are usually more of a danger to the fancy tailed fish like guppies. In community tanks with "nippers" like some tetras (esp black skirted!!) it is usually the bettas that get torn up. They also (generally now--not always) don't like the airflow bubble-things. High airflow makes it hard for them with with all that finnage. I used to breed and don't laugh--show bettas. (Check out the International Betta Congress for more info if interrested) For really fun and easy color in tank, I reallly love Endlers Livebearers. They are closely related to guppies (can even cross with them) and they are easy, bright, active and funny to watch. I had them in with neon tetras, a dwarf cory catfish and an ottocinculas in a 20 gallon tank and I think it is one of my all time favorite set-ups. I am shutting up now...I could go on forever!
Great looking tank--enjoy it!
Amy