Search rdsb in DIY forum. Third or four one down is a really good thread. You may want to shoot the guy a pm to see how he likes it or if it is still running.
I had a twenty gallon hex used as a DBS and fuge for a year or so and found that there was not enough flow to help my system. After a long time the water chemistry in the fuge was different from the water chemistry in the rest of the system. There is a fine line between just enough and not enough flow IMO.