I had one of those cheap glass thermometers break in my sump, I went to adjust the suction cup and it tapped against the acrylic and broke. . The inside actual mercury therm didn't break just the outside and the little balls underneath the wax fell into my fuge. I cut the pump and removed the chunk of moss that the balls fell on to. I also removed all the water in the sump and replaced it just to be safe. I'm assuming they're just lead or something to weight the bottom down? It's not anything I should be worried about? First time one ever broke and I always was paranoid about it happening.