Disease Treatment

[henryriesett]

Hello, I need some help. In my dt, I believe one of my fish has ich (could be something else, need to investigate further). My question is do I only need to put that one fish in the qt, or do I need to treat the entire tank? Thank you, any help is great.

 

[tzabor10]

Usually people recommend treating all fish. Pictures are always helpful
Good luck