Ok... I sold my 125 which was 6' long. I kept the stand and wish to use it in the spot but have it support a 4' long frag tank with O/F tower drilled dead center bottom panel. So obviously I have a 6 foot space to put a sump. I would like to make this sump as long as I can and fit as much rock in it as possible. Also will have internal skimmer. Suggestions on how I should design this sump?