I have a dalmatian molly in a 20 gallon tank with a variety of other fish. Over the past two weeks I've noticed it becoming either fatter or bloated, I'm not sure, and then in the past few days I've noticed that its scales are sort of "pineconing" (as I just read about it in a fish book). I'm not sure what's causing this. All the other fish seem to be doing gine, and the nitrate/nitrite levels are within the safe range. Any thoughts?