Is my beta dying?

Question
I bought two betas several weeks ago. They are in the same tank and are separated by a divider. The one fish, that seemed to be the dominant fish at first, has not been doing so well lately. He has lost his vibrant blue color, doesn't seem to be eating and sort of floats vertically in the water. He spends a lot of time near the surface, or on the bottom of the tank and his gills seem to be very red. Also, his fins look rather ragged. I'm not sure, but it also looks like his eyes seem to be slightly bloated.

My other beta seems to be very healthy and happy.

Help, please! I'd like my fish to have a long life.

Answer
If his gill are very red thats a sign of a gill infection, his ragged fins could be fin rot, and he also could be getting popeye. Your best bet is to change the water in their tank, and treat him with a combination of Maracyn and Maracyn-2. If there is any way they share water even through the divider, you should treat the other fish as a precaution.

Aquarium salt is also a nice addition to use when treating fish with medication. Hopefully, he'll pull through and its really important to remember to change the water once a week, to prevent bacteria and fungus from growing.