I can't say I've ever looked at them under a microscope, so I can't answer your first question ... but that is really cool! Maybe I need to go buy a microscope now!
Are you cycling your tank or have you recently completed the cycle? If so, diatoms are pretty typical and are fed by a combination of nutrients and silica levels. Reducing nutrients (but not to zero!) and turning the lights off for 48 hours usually solve the problem, as does waiting a week.
For Dinos the problem is more involved ... best resource is here: