AARARRAGH!! Help

the little balls are not mercury..(not sure what they are) but if your indicator bar is red its an alcohol if it is silver or greyish it is most likley mercury.

Mercury is not nearly as toxic to fish as it is to humans. When fish exhale through their gills they actually produce mercury. However whether your thermo. was mercury or not.....i would advice you to get the little balls out, perform a good water change 25-30%. Buy new filter floss and media.
Good luck

The balls are just small metal balls used to help weight the bottom end so it stays in the water.