i found a brand new fluval 405 on craigslist for $130. im not sure if it fell off a truck or what, but it was a good deal. my question is, what are some custom media setups people use in these filters? does biological bacteria grow in the sponge or in those cylinder shaped stones that come with it? also, would it be ok to put in activated carbon that i buy in a jar instead of buying the fluval carbon that comes in the bags, or would i need to get some kind of mesh bag to use my own carbon