I have had my goldfishes for around 8 years now, no changes in the aquarium. Tank dimensions is 12 inches wide, around 15 inches tall, and around 32 inches long. The tank is around 40-45 gallons. So the problem is that after my last water change last Sunday, one of my goldfishes has stopped eating and now only rests on the bottom of the tank. It appears to have some strange growth in various locations of its head. Apologize if the photos don’t really help, as it is already hard to try to see the growths in person due to its color and the size. Anyone has any ideas? Thank you.