Hi, what do you mean you used a airbrush in a aquarium? My recomindation is a Paasche H (is a single action) and a small compresser you can get all that for a round 120ish.
If you want VARY cheap Hobby Lobby has a Paasche Air brush and cans of air that is a round 35, it work well for the price but the cone can be sicky but it will loosen up over time.
http://www.craftsetc.com/store/search.aspx...rchTerm=paasche
Has H and the starter but no air as it is to hard to ship contens under pressuer and all.