Hello, I don't know how this works, but I'm going to try anyway....
I have a 50 gallon tank with 5 comet goldfish in it at the moment( I did have 7 until 4 recently died, all fancies. ) 4 out of 5 are still pretty small and 1 is pretty large, about 8 inches long. I was told he's at least 10 years old.the fish I have left have been in the tank for about a year. The 4 fancies I got 6 weeks ago have all died with in a couple weeks of each other. Now my big goldfish has a large tumor thing growing off his side and dark silver scales are forming. He's is a pure shimmering white goldfish originally. My water tested fine.... What can be wrong and what can I do? I really don't want my big guy to die ( or any of them for that matter) and if possible i would like to have a couple fancies in there eventually after I figure out the problem. Thanks for any help!