It is good that you gave us a premise: Freshwater. Since you seem to have not fixated on one species of fish, I will provide you a list of fish that are underrated in the hobby. read more
Best Answer: If you cannot afford to buy a canister filter, you can try looking for a filter that sits on top of the tankor hooks on the top, but I am not sure how much one would cost for a 30 gallon aquarium. read more