the one you see there is a 40 gallon tank....buy it new, so as not to worry about what the guy before you was using it for. measure the dimensions of the ********, and take them down to lowes or home depot so they can cut you some plexiglass "walls for you to glue into place. these walls will create the series of chambers you'll need to house the various items I discussed earlier. Look back at the picture, and start from right to left: the first wall starts at the top of the tank and leaves about two inches at the bottom free so the water has to flow down through the dead coral and back up throgh the blue pad. Build another wall here, but this one can be a full wall that the water must trael over to get to the next chamber. here is where you see the sea weed and mud. move about 14 inches or so down and buiold another plexiglass wall the same way you did the other ( a full wall the water will have to travel over to get to the final chamber. here is where you'll put your submersable return pump. All of the walls have to fit pretty snug in your tank, and have to be glued down with silicone gel used on fish tanks. I had a problem with one of my walls springing a leak, so as a hint, you may want to cut small pieces to uses as braces to help hold the walls up. This will keep chambers from mixing with each other at the wrong time.....i.e. you don't want mudd getting into your return pump area. If you want more pictures, I can send much closer up ones to help you. Let em know :yes: