^^^Like was said, it looks like grains of salt/sugar on the fish, most noticeable on fins. Caused by a parasite. There are many medicines available, but I prefer the salt method(WHich works just as well) - raise the temperature to 27-28 degrees C, add 1 tablespoon of aquarium (NOT table) salt per gallon, and wait a few days... once all signs of ick are gone, wait another 4 or 5 days, then do a couple of 50% water changes, and you're done.