Oxygen

Powerful oxidizers are dangerous stuff!

One I’ve learned about recently (and used) is potassium permanganate. One of its uses is for improving water quality in fish ponds. It oxidizes basically all organic matter. It can simultaneously knock out algae, bacteria, parasites, hormones, and other excess organic waste. And the pathogens it kills can’t build up resistance to it like they would an antibiotic or poison, so it can be used preventively without creating stronger bugs. You can’t really build resistance to BURNING outside video games.

But that also means that if you add too much, you can just as easily sterilize all life in a body of water, including fish and anything else you want to keep.

AND it means you need to be careful when handling it. If you burn your eyes or your lungs, it makes them stop working!