I use Chemi-pure, and also Bio-Chem (Aquarium Pharm.) Both are good, and you can get them at your local pet store/fish store. As for Biological filtration, the sponges you have in your filter offer a little bit of biological filtration, but not much. If you are looking for better filtration, I would go and get a canister filter, there are many options for all kinds of filtration you can put in them!!!