I have in my tank 1 cleaner shrimp, 2 common clowns, an algae blenny, a watchman goby, 3 blue-green chromis, a sea urchin and numerous crabs and snails. Every third day they have frozen mysis shrimp that comes in cubes about 1cm square, how many should I feed? - I know not everything eats this but thought I'd let you know what is in tank!
Generally, if food is not gone in 5 minutes you're feeding too much. That's not a hard fast rule though. Watch your tank to make sure that everyone is eating.