Yes and no to the BioWheel question, laura. Some of the good bacteria resides on your BioWheel, but not enough to make a difference. The majority of it resides in your filter media. Honestly, the whole "replace your cartridge every three weeks" is a marketing ploy to make more money. I had an Eclipse 1 system (18gal tank) and I have an Eclipse Hex5 tank right now, both with the BioWheel. As soon as I'd change the filter cartridge in either tank, everything would go all haywire in the tank (this was back before I knew about cycling and not changing filter media, etc) and I'd get horrible algae and have some seriously unhappy fishes.