I have a comet that is 6 years old, about 9 inches long, that is living in a 100 gallon tub. Also in the tank are 3 other orandas, only about 3-4 inches long. The comet recently developed some sort of gelatinous junk under his gill cover, and the scales are turning silver/white around it. The fish are normally in a pond, but are in for the winter. I use a sponge box filter and just did a water change less than a week ago. All water parameters checked out fine. Nitrate is just above 0, so I'm going to do another water change. Any ideas as to what it could be, or how to treat it?
I appreciate any advice or comments! Thanks!