Help! I have 3 blue gouramis. Two of them have some sort of sores on them. The one is on the top of his head, and on the other on the top part of his gills. The aquarium store said to use Melafin. Anyone know if this is correct or anything else I can do? Do I need to quarantine him? I have a 55 gallon tank, w/ about 15 other fish. I don't want this to spread to my other fish. Any help is very much appreciated! Thank you.