How to figure out how much to feed your (single) fish?

[kingkapoor]

I have a 1.5 inch Hippo tang in a 50 gallon. How do I know how much to feed the guy?
I give him about half a cube of emerald cusine and he seems to like it, doesnt really care about the nori I put in for him, even with selcon and garlic soaking

I have a 2-3 inch Foxface in a 20 G quarantine, who eats nori, nothing else (but he is new), how much nori do I feed this guy?

I have a single damsel in a pico tank (5 gallon), how much do I feed this guy?

 

[Big G]

Consider trying again to feed the nori by cutting it into narrow strips on a clip, etc. Works pretty good on smaller fish.