I don't understand your aversion to tangs. I just got a yellow the other day (a few tense moments with the yellow rim, but they're buds now) and he's constantly on the prowl for green stuff.

The hippo, naso, and yellow rim (to include the yellow) eats the grape culerpra... and I did have a foxface that really LOVED grape, but he also liked the zoas.

Not sure if my starry blenny would eat grape, but he's always sponging off the algae from my glass... and fat for it too.