If they are suffering from an infectious disease, the whole tank including healthy tankmates will have to be treated. Isolate the sick fish only if it is being bullied or stressed by other fish.
You have just read another great aquarium blog post by iQuatics. If you would like us to blog about a specific subject or have your own aquarium blog content you would like published on our website, get in touch. Together we can help grow the iQuatics aquarium blog into a vast resource full of combined industry knowledge.