:-/Hi guys, I'll be using a plenum in my main tank with a 4" deep sandbed, thanks to Bob Goemans, who's really helped me decide it's something I'd like to do. It's really cool that he e-mails you, too! Anyway, I have an approx. 12-gallon refugium, and I'm not sure what to put in it or how deep to make the sandbed. I kind of like the idea of using plain kitty litter. I'm hoping to use the 'fuge to grow some macroalgae. What do you guys think?