My molly has changed color and keeps sitting on the bottom of the tank?

Question

When we got her she was silver with black spots now she is turning more black with silver spots she is the only one of her kind in the tank but keeps dithering on the bottom of the tank

Answer 1

When a fish turns a darker color, it usually is a sign of too much ammonia or nitrite in the tank. Lethargy is another symptom of this. I'd suggest a 25% water change and see if her behavior changes. See ammonia and nitrite poisoning in this link: http://www.fish-disease.net/diseases.htm

Another possibility is that the activity and color change are separate issues. Mollies go into "hiding" when their about to give birth. If your molly seems to be more plump than when you bought her and has a "square" look to her abdomen, she may be close to not being the only one of her kind anymore.

Also, if there are other fish in the tank with her, make sure she isn't being harassed, or has plenty of hiding places where she can get away.

Answer 2

sounds like stress
..but the others are ok?
do a 25% water change with dechlorinated water.
is your filter mature?
has your tank been running for at least 3 weeks?