I suspect your Goldfish plant has Whiteflys based on your description of the insect. Repeated cleaning of the foliage will dislodge the various life stages present. The whole lifecycle from egg to adult is about 16 days. Repeated cleaning (more than once a week until you do not see any stages of the insect)is necessary to break the life cycle. If you have other houseplants, be on the lookout for Whitefly on them too. There are houseplant insecticides available too. Use them carefully and in a well ventilated area.