You're right I can't see the spots regardless , goldfish are cold water fishes so if you do raise the temp, don't leave it too warm for too long. Could just be some stress issue with your tank chemistry, or tankmates harassing bubbles. The best teacher is your tank. Watch closely for awhile & look for anything odd. Also goldfish are pigs & produce ammonia like crazy. Do very frequent water changes and keep an eye on those spots.