If you are absolutely sure that water is good (ammonia and nitrites at 0 and nitrates at less than 40), it could be that this is some natural coloration. My golden has very tiny (even smaller than these) dots on his face that he started getting when he was around a year old (I don't know exactly how old he is, so this is an approximation). When did they develop? How quickly? Has anything happened recently that might have stressed it out (you moving to a new house, different water source, new pets, etc)?
You did mention though that the temperature is a little high; how high is it?