Why is it that people come on here and ask for advice, get it, then question it? That always confuses me.
2 pumps and no overflow = flood. Not if, but when. 100%
I'm not here much and it's comments like these that drove me away. Somebody asked why this forum has slowed down and I've seen this over and over here. How does this help the op?
Cuccaro - I had a 55 gl with the same set up. Why not use a hob filter as a refugium? I did and the only issue I had was the noise from the water flowing back in the tank and bubbles it caused. I couldn't raise my skimmer higher out if the water to maintain its recommended water level bec of the trim on the tank. I'm sure I could have come up with something to deal with this, but I ended up getting a larger tank and sump. This way theres no chance of a flood. With my set up, small pump pulled the water in and it overflowed naturally back to the tank. If it failed, there was a small amount of water that flowed back in.
The comments on 2 pumps and a flood are correct with 2 pumps. If one fails, the other tank will flood, you could actually drain your entire dt. Let the water siphon out of the dt and then pump it back up. You still run a flood risk if the pump fails and the water continues to siphon into the Refugium, therefore you would have to keep the water level at the appropriate level in the fuge. You'd also have to find a pump that meets the flow of the water going into the fuge and would likely need a valve to control it.
Hth!