Hi, I had the same problem, and it all seemed to happen rather quickly. Stanley my 14 year old goldfish developed black patches 3 weeks ago including a funny geometric shape under his skin on his head. I checked out the internet, some said it was normal colouration changes and others said it was ammonia in the water. He also seemed a bit thin though he was eating. So I did a 50% water change, cleaned the filter put in a fine filter, dosed the tank with anti internal bacteria and did the same 4 days later. The black patches didn't disappear but my fish seemed absolutely fine and loved the peas. However, yesterday I noticed Stan swimming in a banana shape and being erratic. I took him out and put him in a hospital bowl, added the same treatment plus aquarium salt but 24 hours later, after trying to rally and much time spent with me holding him upright to breathe properly and get full advantage of the treatment, he died. Sad. He knew who I was and would respond to my voice..I had him a long time. I hope you have more success than I but bottom line is act quickly. My question is had I not responded quickly enough or was he just too old to pull through? Anyone?
