How do I tell if my Mandarin is getting enough to eat?

[Kit with Cat]

My tank is 90G, HOB fuge, the rest of the tank mates are:

Bicolor Dottyback (do they eat pods too?)
Hippo Tang
2 x False Perculas
Diamond Goby

I can't say he looks fat so far..but he's doesn't look sickly thin? I've been thinking about getting a melanurus wrasse (to get rid of red planaria..which I was told the Mandarin might also eat)...is this advisable?