His immune system is a bit weak right now from the stress of being caught, bagged, and placed in a new home. In my experience most tangs will inevitable get a slight case of ick when first introduced. Just keep and eye on it and do your best to keep stressors to a minimume, keep good water quality, and keep it well fed so that it can restrengthen it's immune system. As stated above also, soaking food in garlic helps also. Good luck!