easy way to tell if its dropsy is look at it from the top..... does it scales look like a pine cone..... there are meds for dropsy but generally its fatal.... you really need to move the fish to a QT.... it also could be just bloating from over feeding, try feeding it some blanched peas.... so it that helps with the bloating

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Gold Coast Aquarium Society South Florida
www.goldcoastaquarium.org