That is correct 90% snails.. From an expert and personal experience, that balance should keep their teeth in check far beyond 6 months.
I agree:
"Is a puffer species that does not readily adapt to captivity" but some have done it. I am not certain what their individual circumstances were, but I tried a 210 long, with unidirectional flow, and it didn't work. They are currently in a 55 with higher unidirectional flow and it is better but not perfect.
I also agree that mine do seem to like the pleco algae chips also ... that is not a bad thing. I just thought it was strange. After your comment it doesn't seem so strange