Um...I wouldn't put any fish in there.
What would be the purpose?
It sites in the back of the tank where you can't see anything.
Besides, a refugium purpose is to house critters, pods, worms, macro algae for your tank.
Just put some live sand, brittle worms, spagetti wrms and some capelra in there. That will be benifical to your tank.
If you fell a need for a fish. Put him in the main tank.
Not your fuge.
Fuge is too small for something like that anyway.