Return pump too strong for overflow.

Does the pump have a dial on it to cut back the flow?

I usually only use one line for a return to the tank and use a ball valve to govern the amount of water into the tank, also pumps should never be run wide open and should have some back pressure on them. I do like Tuckers idea of dumping it back to your sump depending on your flow rate of the sump and what you are doing with the sump. Maybe a setup with a line running to the tank and a branch off that are both controlled with ball valves.

Where did you learn that pumps should never be run wide open? Every bit of info I've ever been told or read goes against what your suggesting. It's pretty much common knowledge that when you start restricting the flow on these types of water pumps that they can generate stray voltage and excess heat. Both of which are bad things to have in a reef tank.

Derek, if your main pump has a larger GPH capacity than your overflow can handle then I would suggest putting a tee fitting at the output side of your pump with ball valves at each output. One line then goes to your display tank and the second auxiliary line returns back to your sump and acts as a pressure bypass. This way you can still have your pump run wide open and still control the amount of flow to your display tank. The added flow through your sump is beneficial as well for suspending sediment for the protein skimmer to remove.

I'd add another overflow box. I like lots of flow through the sump. I've had way better luck long run this way.

So what about when your running a reactor? You kind of have to dial back the flow. If your running gfo you definitely have to dial back flow.
Is this not an issue because the pump is smaller?

I guess I will get another overflow asap. I need to get this tank full of water though. I have too much rock in my 55 and it looks awful! I guess my plan is to get a tee w ball valve for now. Then in the next month get another overflow get rid of tee!