A friend of mine has 3 fish tanks at home. One houses a couple of dwarf pea puffers, another has a male betta, and the third has a red-eyed puffer.
She phoned me in a panic yesterday because the thermometer in her dwarf pea puffer tank had broken, and there was mercury all over the place in the tank and she couldn't get it out... she wasn't sure whether or not it was safe to keep the fish in the tank with all of that mercury, but would also be unable to move the dwarf pea puffers in with either of the other fish.
I told her I didn't think it was a good idea to keep them in the tank with the mercury, and suggested that as a temporary solution, she could set up a bowl for the betta with some of his tank water and some of his gravel, and move the dwarf pea puffers into the betta tank for the time being. I figured out of all of her fish, the betta would probably be the most hardy. And, I hate to consider this a factor, but the betta would also be the cheapest and easiest to replace, since the puffers were all special orders... seems callous to think of the economic side of things when they're all living creatures, but it's still true. I stressed to her today that the betta needs to get back into a tank ASAP, or at the very least, she should have a heater in his bowl... hopefully he's not too upset about being rehomed for a short time.
Today she was talking about how she was having difficulty getting all of the mercury out of the tank... she worked at it for 4 hours and still couldn't get it all out.
Is it safe to put the fish back in? Should I tell her to just dump EVERYTHING and make sure it's all gone, and then start over? Is it safe for HER to be around it, even? Mercury scares the crap out of me... and I think it's better to be over cautious, but how much is too much caution? I don't want to be overly paranoid about it and make her go to waaaaaay too drastic of measures, but I don't want to tell her it's all fine and dandy if it isn't.