Discus, all but 1 is eating & getting skinny?

[SonicsDC25]

I currently have 3 Discus in my 55g and 2 are very active, healthy and eating well. The last one the color has really faded and he doesn't eat, while getting skinnier by the day. First off, is it contagious? Because I need to know before it spreads to my other fish. Secondly, how should I treat him? I don't see him poop much because obviously he doesn't really eat much, so there's nothing to come out

 

[Crony]

Been there

That has been my experience more than once. It seems the dominant, usually the larger pickes on the rest and sometimes the most on the smallest one. If that one starts getting stressed, then eventually he'll get sick, all that you mentioned. Best to remove and put in a sick tank which you should always have especially with discus. In the sick tank, raise temp to high 80's, I've heard even 90, 92. treat with metronidazole and/or praziquantel. I used "General Cure" by API, treats parasitic fish disease. It has both. I think it was from Pet Smart. Feed him until he gets a bit bigger and reintroduce back. You may even want to add one more with him when you bring him back. Give it a whirl.

 

[SonicsDC25]

That has been my experience more than once. It seems the dominant, usually the larger pickes on the rest and sometimes the most on the smallest one. If that one starts getting stressed, then eventually he'll get sick, all that you mentioned. Best to remove and put in a sick tank which you should always have especially with discus. In the sick tank, raise temp to high 80's, I've heard even 90, 92. treat with metronidazole and/or praziquantel. I used "General Cure" by API, treats parasitic fish disease. It has both. I think it was from Pet Smart. Feed him until he gets a bit bigger and reintroduce back. You may even want to add one more with him when you bring him back. Give it a whirl.

There's only 3 Discus in the tank though and there really is no dominant one. This one just sits next to the filter all day, really hope this isn't contagious...