IME, the store bought bacteria is not any good, I would stay away from it.
As far as which filter you choose, an external hang on back filter will filter the water just as an internal filter and a cannister filter. I prefer the cannister filters myself, I think they are more efficient and I don't like the way an hob
looks or the sound of water flowing into the tank.
You can add different filter media to it, such as bio rings, sponge, floss, etc to give the good bacteria more places to attach. Your tank needs to go through the nitrogen cycle.
Check this link out http://www.aquariumadvice.com/forums...es-103339.html