I'd love to use an actual tank 20 or 30 gal but no place to set it near tank... so plater hanging box it is... beautiful setup thoI use old 20- 40 gallon tanks for this purpose, sometimes on a shelf sometimes in window boxes to help plant growth. Sometimes the water would return straight to tanks, sometimes back to sumps.
the one above is a 20 gal with papyrus and aquatic plants, and also acts as a refugium for shrimp, and sometimes for fry.
below a 40 breeder on a shelf, with papyrus, Pothos and is where I wild put expectant female live bearers, to drop fry in a secure environment