cotton like substance on new butterfly

[bzolnowski]

hello, i have a new butterfly and angel in a 28 gallon hypo. they have been in for about four days. the butterfly has a small cotton like substance on his back fin. he seems to be doing well but mostly eating only black worms. any idea what it is?

 

[beth]

It could be Lymphocystis? Thise disease is not really treatable with medications but can be controlled, and virtually irradication with good tank quality and a good diet and happy environment for the fish.
Keep an eye on it, it could be a parasite. More info or further developments is needed. Do you have a pic?