I made a sump filter out of a 10 gallon tank. I have a hang-on-tank overflow box for it. I bought a pump at Petsmart and it just doesn't have enough power to lift the water from under the main tank. So, I have had to put the "sump" next to my main tank so that the height that the pump has to move the water is only about 2 feet. I am getting ready to move (which is another concern in itself ) and I don't want to have my sump visable in the new location. I considered getting a ready made sump but with all the house stuff, I am not ready to upgrade completely yet. So, I would like to get a different pump for now so that I can put the sump under the tank where it belongs. So, my question is, what kind of GPH do I need to lift the water and have sufficient flow? I would need to lift the water about 4 feet. I have seen the different ratings on height of water lift on certain pumps, but I am not really sure how to know how much flow I need. I am also anticipating a question from someone on the rate of flow from my overflow box and I don't know that, unfortunately. I am guessing, however, the the flow will increase once I have gravity working for me and the water is going straight down. Right now, the water has to travel up from the overflow to get to the sump. Any help or advice would be very much appreciated!!! Thanks!