I have an iwaki wmd-20rlxt and I just noticed yesterday that the return line is only 1/2"... I have one 1" corner overflow so I Am guessing that this pump is undersized for my tank. I am in the process of building a sump so should I grab a mag 9.5 and use that instead of the iwaki? My return pipe is slots cut in it and the water level is about 4" below the top of the water in the tank.