1.- Heater 2 -bag of purigen on the top. After the water passes through that, it flows onto my chaeto and at the bottom of 2nd chamber is where I keep a bag of chemi pure elite. By the way, I removed the false floor of chamber 2. It allows additional room for modification. And in the 3rd chamber there is nothing but my upgraded pump. MaxiJet 900. I removed the sponge. I did these mods after careful consideration to what I thought my tank needed. This worked for my tank. As the tank matures it requires different things. And every tank is different. Depending on ur CUC, corals, fish, etc. I've heard some people say the stock bioballs work fine. Who knows?