Fin and Tail Rot

Hello,
I'm new to this forum and wonder if any of you might be able to help. I have 3 Goldfish that my sons brought home from a fair almost 4 years ago. They were tiny feeder fish and have grown into beautiful Goldfish. They are in a 30 Gallon tank. I just noticed that one of them has fin and tail rot. I have Maracyn Two on hand, but I wonder if I should treat all 3 or just remove the one and treat it in a hospital tank? Does the main tank have to be treated also? Should I add Salt to the Maracyn Two? Should I remove the Filter Carbon? The instructions say to keep normal filtration, but I always heard to remove the carbon? Any answers are highly appreciated. Thank you so much, Fonzie

 

I'm not knowledgeable in FW systems, you may have better help in the freshwater forum. But it is true to remove carbon, as that will absorb any medications in the water column. I would treat the tank with your Maracyn to kill any possible free floating forms that are causing the fin rot.

 

Thank you for your reply.......I didn't realize this wasn't the FW forum LOL...I will post there now.