Awesome tank!
I was thinking of doing something similar, but with a tank maybe half that size.
I also breed nano fish and I have a 120 tall (really weird dimentions, 5 by 1.5 by 3) wich I keep a marble motoro in. I've fallen in love with that one fish and I want to sell all my little fish and the 25+ tanks I have dedicated for rare dwarf cichlids, goodeids, and plecos and get a 300 double deep, move the ray to that tank (and of cource, get a few more marbles ) and have 1 wetpet in the 120 or (if I'm lucky) make the 120 a stingray pup tank.
Once you have it all setup, let me know if it's worth getting rid of your nano fish
Wow that's a very nice big tank. Too bad my dream is crushed by a 90 angle flight of stairs to the basement. No windows either. Have you looked into a water softener?