I have to agree with Raver. While I don't use Physan 20 made by Maril Products, Inc, 320 West 6th Street, Tustin, CA 92780 1-800-546-7711, I do use the competition, SA 20 made by Southern AG. It is EXACTLY the same chemical formulation. For use on orchids as a disinfectant, fungicide and algae control, the recommended concentration is 2 TEASPOONS / gal of water. I spray everything in the greenhouse; plants, pots, benches, greenhouse glass and floors about every 3 weeks or so.