If your tank is planted then you don't want too much water surface agatation becauseit will deplete the co2, a hang off the back(HOB) isn't my first choice. If your tank is planted, canister is the better option. If your tank isn't planted then your best (and most expensive) option is a canister wet/dry, it breaks down the ammonia and nitrite much faster then conventional canister or HOB filter. But If your on somewhat of a budget then I would agree with IceH20, good choice.