Originally Posted by Pasfur
It is not possible for water to enter the sump at a faster rate that the sump pump pumps. Physics prevent this.
"How much sump would a sump pump pump if a sump pump could pump sump?"
Sorry Pasfur, I read your comment above and thats all I could think of
can you use a pump to power your skimmer with a return into the tank or will I need 2 pumps?
well, I suppose it is POSSIBLE, but there are a couple of reasons why I wouldn't suggest this: (1) most skimmers, even really high quality ones, have microbubbles in the output of the skimmer. The baffling system in a sump generally is in-place to trap these bubbles and prevent them from returning to your display... they aren't dangerous, but they aren't very attractive in the display. And (2) most skimmers have a certain rated flow, and it might not be sufficient for a return from the sump to display, it could depend on how you plumbed it though. Alternately, some skimmers don't allow any plumbing on the output, at least any plumbing that prevents the output from draining freely.
One way I COULD see this working, is purchasing a single, large/powerful pump, and splitting it's output... have it drive both the skimmer as well as the return plumbing to your tank, but not the skimmer in-line with the return... have the skimmer's output directed back into the sump. I have heard of people using a single powerful pump to power their whole system, by driving the pump into a manifold and tapping off it for whatever they want to drive (skimmer, UV, reactor, chiller, return, etc... probably need to use valves on each tap to control the amount of flow through each).