newbie,
honestly, be glad you were able to get him to the two month mark. just picked up your post now or i would have tried to respond earlier. what your fish was experiencing could have been anything from bacteria to viral.
point is, try to avoid potters. they are endemic to hawaii only (but then u knew that) and have very specialized feeding habits, almost exclusively sponges. while spirulina and brine might be ideal for most salts, potters are very specialized.
i have known no one to keep these fish successfully, although i am sure some have. they are gorgeous, no question, but do resist the temptation to get another one.
good luck to you.