Hydrogen Peroxide
This common product found in drug stores and supermarkets, at 3% concentration, is a natural treatment for algae, gray mold, Pythium and powdery mildew. Using hydrogen peroxide on your marijuana plants will not bring them harm. Peroxide helps aerate the soil by adding oxygen and is both anti-fungal and anti-bacterial. Cannabis plants can be fed a mixture of hydrogen peroxide and water as a fertilizer and disease deterrent, resulting in healthy plants. It can be misted on the leaves and/or applied directly to the soil. An easy way to apply is to fill a clean fertilizer spray bottle that attaches to a garden hose and feed as you would, say Miracle Gro. The bottle will have gallon markings on it. Fill the bottle with peroxide. When you turn on the hose, it will automatically dilute. If feeding sick plants, add one cup 3% hydrogen peroxide per gallon of water. Pour into a spray bottle and spritz the leaves, making sure to cover completely. For general feeding, add one half cup to a gallon of water.
Hydrogen peroxide can also be added to the water in hydroponic environments. It can be used to sprout seeds by adding it to the water they soak in before planting; they will sprout quicker and grow stronger. Follow the general application recipe for the peroxide to water ratio if using to soak seeds.