Goldfish strange behavior?

This could be skin and gill flukes. Fish should be removed to hospital tank-main tank should be disinfected and reset up. A very careful, very quick dip in saltwater(for freshwater fish), can possibly cure it, but fish can become stressed very easily. If you don't want to chance this method, get an antiparasite treatment for tank.----If the fish have Ich, you will see white spots on them.