I have decided to go with the 20 long as my sump. The 30 just took up too much room under my desk and I really didn't want to relocate my paper shredder.
The blank is just a standard 20L 30x12x12
alt="" />
I wanted to build the sump with a display style refugium in mind so I divided the sump in half using the entire front portion for the fuge.
I purpously possioned the float valve high for maximum water volume and to give me just a little more time refill my top off container. It cuts the water off when the last compartment is 3/4 full, thus leaving plenty of room for the 3/4 gallon back siphon that will occur when my return pump is off.