One of my zebra danios in my 10G hasn't been eating and is acting awfully lethargic lately. He stays in the corner by the heater, just a few inches below the surface. During feeding time, he doesn't make any effort to get food, mainly nips at what floats by him.
The rest of the danios look fine, have been eating and swimming about, and bugging my tetras as usual.
So, should I flush the poor fish (being that they're pretty inexpensive) or try some medicine?