New to setting up a sump for a 120 DT. Have to take down the old 120 and get the new one inplace asap for my livestocks sake. if the return pump move say 500gph and the skimmer is rated for a tank even larger than mine but moves 180gph how does that accomplish anything. Doesn't all the water have to move thru it instead of on down to the pump area where is immediately returns to the DT. I've never in 35 years had filtration outside the tank and I'm terrified but I have a seam slowly failing on my current tank.