I just broke my floating thermometer. The actual thermometer is intact and noting leaked into the tank. However, the glass broke and the black pellets fell to the bottom of the tank. I used my magnet cleaner to get as many of them as i could. I would imagine that this is nothing to worry about as the really smart thermometer makers chose to make these things out of materials that would be inert if introduced to our tanks. Tell me I am right and I dont really have to go in there and attempt to scoup out some sand all the remaining black pellets.