Just leave them. They will eat detritus in the tank therefore processing the waste down a bit.
If it's only on top I would guess he is burning from too much light.
gobys and blennies. sixline wrasse is a good fish for a nano as well. blue chromis, blue devils
I have not heard of many problems with puffers other than their lack of manners when eating and their size and bio load. They are not usually the aggressors