PlanetCatfish.com

I got a fairly large arrowana late last evening. I was worried that my Pseudoplatystoma fasciatum was going to try and eat him, even though it would be quite the mouthfull. Well this morning I awoke to a dead arrowana that looked untouched. I am assuming stress caused the death.

This evening I noticed the paper for my stick on thermometer was on the floor of the tank. The glass and tube for the thermometer was broken. Is the red stuff mercury? If not what is it? I am worried about my fish...

If it's red, it's alcohol. Mercury is silvery, and mercury poisoning is chronic (meaning that the fish would not have died so quickly).
Depending on the size of your tank, the effect should be minimal. A water change would be good, though.