I am noticing that one of my White Cloud Mountain Minnows is acting strangly. It was swimming head up right into the current. Then I came back today, and it was sitting on the bottom of the tank, completely inactive. One side of its scales are all puffed out like a bunch of teeth, It looks really sick, what is it? Is it dropsy? How can I remedy this/prevent it in the future? Should I put the minnow out of its missery? Will this spread to the other fish in the tank?