fish get diseases im not sure whqat this is called but you can buy better food and a chemical you put in the tank once a week and it should cure soon. go to the pet store and they can help you
It's certainly not okay! Fish have scales for a reason. They usually lose them to disease, parasites or bad water quality. Can you tell us the Ammonia, Nitrates and Nitrites of your tank? Has he been scratching himself of anything? Any other signs? Fin damage?