I took 3 comet goldfish out of a backyard pond and put them in a 29 gallon aquarium I had set up for them. Thought I did everything right when setting up the new aquarium, but within 3 weeks, the comets developing black patches on their sides and fins.
One has died already, I don't know what to do to save the other two. They are not eating and are swimming erratically (when they move around at all).
