hundreds of white spots on glass

It is most likely a type of tube worm. They are good for your system, and a sign of a healthy tank.

GMan is right , it looks like a flavor of tube worm perhaps. And if definitely a sign of a healthy aquarium. I have a very similar situation. I had a rock come in that was completely infested with tube worms, and when I say infested, we are talking literally 30 little tube worms popping out of every hole imaginable, never seen anything like it before. Now they have spread all over my tank, easily have to have well over 60 little tube worms in my tank now.

now that i have seen what your talking about, they look to be hydroids. they dont cause any major problems, may sting your fish however. never had to deal with them myself, but i read they usually dissapear on their own.

you should probably do a google search on them, but i wouldn't worry too much.

I had the same thingies when I just set up my tank. All I did to make them go away was to clean then using a sponge. They do come back but in muuch smaller numbers. Then you clean them again and show them who the boss is

Hydroids typically won't survive in a tank for too long. They aren't the most desirable thing, but nor are the considered a pest. Harmless, in the long run, and probably only present for the short run.