Overflow box question

[humuhumu1]

I have a an overflow box with two u-tubes and a pump rated at 1200 gph. My problem is that when I have one of the u-tubes running the water level stays the same, but when I start the siphon on and the second u-tube the water level rises in the sump. Basically, the overflow box is outpacing the pump and the sump would overflow if I let it go. How should I go about fixing this problem. Thanks.

 

[nemo22]

it could only be one of two things. your overflow box is to low in the tank, or your pump is not strong enough to keep up.

 

[humuhumu1]

I don't think that the overflow box is more than 1200 gph. The overflow box was almost or completely filled, so should I raise the overflow box so it isn't completely full.

 

[nemo22]

yes, you have to ajust the overflow box to match the speed of the pump.