Clown,blue tang ,black and white heniochus and yellow tang all small to medium size and three snails and 5 crabs
3 of these are pretty big fish...... that poop a lot!
Are you feeding any nori or algae sheets? Algae should be a major part of at least the tangs diet.
I would recommend feeding a 1/2 sheet of nori every 2-3 days and cut the cube feeding in 1/2.