Not sure why you guys are preaching all this chemical warfare when just putting the rock in fresh water will accomplish the same thing with a lot less toxicity.
Also, since the bacteria the take care of the nitrogen cycle are the same in fresh and salt, a fresh water soak will at least stabilize it in terms of biological capacity. The only thing that will be left are good bacteria. Plus, if the water is circulating, the die off will be faster than drying it out.
Surprised nobody has told him to use gasoline and a match yet.