He did, that's why he asked, "What would everyone recommend to give the fish to get some veggies in their diet?"
As for vegetables I'd suggest spinach only because that's what I've fed my herbivorous fish in the past, however, I'm not too sure how the convicts will react to it. It can't do much harm though, so I'd definitely go for it.
I know you didn't ask this, but I would also DEFINITELY look into getting some other fish in there. Convicts do not need a 75 gallon tank to themselves as they stay relatively small. With this size tank, it's almost as if you're just wasting space if you just keep two convicts in there, but if that's what you want, no one's gunna stop you :-D
Hope this helped...