Sorry. Mondo grass is not a true aquatic meaning it will just die if it remains submerged for too long. Too bad because it is pretty and looks nice in the aquarium.
Yeah, I just fell for PetSmart's Mondo Grass too, i thought it would look great in the tank. The girl even said that it does great in the tank and they normally don't get such nice pieces in. It dies!! :rant2:
Try some dwarf sag. or some pygmy chain sword. I got some dwarf sag that is doing really nice in my tank, and it looks sort of like mondo grass. I think this is it http://www.tropica.com/default.asp.