I have a goldfish for 26 months now, and its alone in the aquarium that takes around 10 litters of water, we feed him with proper food for goldfishes and no plants with the aquarium just some stones, the water is changed in a regular basis and when we do it we put some product to balance the water, this week I've noticed that a purple spot appeared on his head, and im quite worried about it, I've been googling to try to find what it is, Im from portugal and here we don't have vets that know about fishes, at least where I live. He is eating well, and behaving in a normal way, no other spots on him, and the he seems fine except for that that I dont know if will evolve in the next times. I will upload some pictures and If anyone knows what this is I will appreciate the help. I never had a fish before and I actually became quite attached to it, he comes when i call him and he learned how to make noises lately, and I really do not want to happen something.