Having 1 pump in and 1 pump out of a tank is sure disaster. While both powerheads my be the exact same make and model having two that pump the same amount is almost impossible. The best thing to do is setup an overflow drain from the main tank down into the refuge. And from there a pump to push the water back to the tank. The other alternitive would be to pump the water to a refuge above the tank and have an overflow gravity down to the tank again.
There is a link in the DIY
forum about how to make a small overflow out of those lee specim contaners.
Ideally you dont want to light your refuge 24X7 anyway. I suggest a reverse lighting setup where the refuge light is on when the tank lights are off. This might not work given your desired refuge location. In that instance you could time the refuge lights with your tank lights but you would lose the PH
balancing aspects of the fuge.