Safe Additive for Procarbonate

[Raider84]

Im using a procarbonate res in my future setup, and i've heard that anti-freeze is a embrittlement agent to acrylic and procarbonate.

So my brief question is what is a good addictive that is safe on plastics, yet still lethal on the critters?

[walkerIV]

Any aquarium shop should have some bacteriocide that is safe to use in aquariums.