im new to this so you have to get me some slack LOL . i have a 125 gal with two built in over flow boxes . its draining into a 25-30 wet dry sump or filter whatever you call it . what am i suppose to put inside . i know you need to put a layer of filter pad and some bio balls . there is a another slot where it slides what am i suppose to put in there carbon??? i also left some ceramic rings on the bottom since they were sitting around . why do people say bio balls are not good and they say to use live rock or sand . could you please help me remember im setting up a fresh water tank . thanks for your help