I have a freshwater refugium on my 120 gallon. It is a 40 gallon with duck weed and valls. It works great to help my Diy plastic kitty litter wet/dry. In the bottom is plant substrate but the duck weed took over and choke most of my valls out. I would use a hydro pot from the "pot stores" filled with small lava rocks to hold the roots in the water. The hydro pot could sit in egg creat, plastic, or acrylic over the sump. I got fancy with my show tank and drilled 12 3" holes in glass lids to grow strawberries. Aquaponics is very cool to do with your tank.
That is awesome. I was thinking eggcrate laid a cross top and letting roots dangle through. Could you post A pic or five lol. Where do you get lava rock out of season anyone know?
Exo-Terra makes a lava rock substrate used for a drainage layer in reptile tanks called Bio-Drain, it is smaller pieces of it than you'd find at a landscaping place, but may be a good last minute option. I believe it comes in 10 pound bags and after a good rinse should work pretty well for what you're doing
