I have a clown and blue regal that love the stuff as well. I put a sheet that is about 1-1.5 inches wide and 5-6 inches long..I would think since you have 2 fish that this is primarily their niche food, I would put more than what you are in there. Fold it into a tighter square so it doesnt get torn as easily. Plus if any does float away your clean up crew should take care of it.
Also if you want to add a little punch to it, put some vitamin C, selcon, Zoe, good stuff on there. Not a lot as a little goes a long ways.