So i have had a 50 g that I have been just running without doing much with it. When i woke up this morning the pump was almost running dry and the tank was almost overflowing. The over flow was just as full as the tank, my drain type is a durso it was completely submerged. It does return water to the sump at a good pace, but I'm guessing its not going as fast as usual but I can't figure out what else could be causing the problem. The main pump seems to be working as it returning water at the regular pace. I stuck a hanger down the durso air hole in the overflow to see if I had any blockage but that seemed fine. Anyone have any ideas that maybe I'm missing here.......