Hey,
I'm setting up a tropical tank. I only have one fish for now, to start the nitrogen cycle going. But for some reason there are these white dots that are clumped together. They looke like white fuzz, it's not very visible unless I turn on the light. However they are only appearing on the heater suction cups (which are made of rubber) and on the suction cup of the thermometer (also made of rubber) nothing else. What could this be? Thanks

Try just wiping them off with a paper towel. That sometimes happens in my tank on the suction cups, I think it's some type of mould.

Hey,
That's what i thought it was, but i wasn't sure. Is it harmful to the fish?

I haven't had any problems with it, I think it's pretty harmless.

Do you are have you used salt in your tank? mine used to get little white dots when the water splashedaround on things and left a little salty residue which like fishmerized said wil wipe off with a damp paper towel. and if they won't come off with that gently scrub with dampened algae scrubbing pad

You often see that in the beginning stages of setting up a new tank,or when you often do big water changes on an established tank,and it is all quite normal.Kind of like the first stages of Algae,or The building of the bio-bugs. I tend to keep the front glass clean,and let the rest of the tank do it's own thing.