The filter mechanism out of the little three-gallon aquarium where the betta is. It tends to pop out of its suction cups and float on the water. It's done it twice tonight. As a result, it is no longer pushing water over the filter's lip, so it really isn't doing anything useful anymore. If I can, I'll replace it soon. In the meantime, the fish will have to be content with water changes and a large bubbling air stone.