Fast him for 2 days. If he doesn't get any thinner, do a Epsom Salt Treatment in a QT tank for 12-14 days. It's 1 teaspoon of salt for each gallon. You could always just fast him for a day and feed him frozen daphnia, it's a normal laxative. :) Next time, just make sure to feed him less. Good luck, are you sure he's not just bloated?
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