Giant Danio's are great dithers, they're fast and too big to really fit in the mouth. I'd say in 5-8 months you'd want to look into a much bigger tank though. About a 75 gallon. Dempsey's aren't an overly aggressive fish as a rule, but cramped they get nasty as will most larger cichlids. You also want to make sure you have more than adequate filtration too.