My mbu puffer of two yrs has a small spot on the left side of his face. Looks like a burn or bite not sure. Tank mates are an endi bichir and sting ray plus a gourami. Tank is kept at 82 degrees 150 gal did water test and there are no traces of a ammonia, nitrites. I am treating with pima fix and plan too do water changes every 3-4 days to aide in healing. The puffer did not eat tonite and that is when I made the discovery of the injury. For a week or so the puffer has been hiding his head in the under growth. He came out to check out the tiger shrimp i feed him normally from a skewer. But did not attack them at all. Please help any good advice is welcome thax.