H2O2 or peroxide is used as an oxygenator and antimicrobial. It kills bacteria good and bad, it also delivers oxygen to roots, which is very beneficial. When they talk about using 2 tablespoons per gallon of water they are forgetting to tell you it is the 50% food grade kind, not the 3% solution you find in the first aid section of the nearest wal mart. It can be used in soil, but much more common in hydro. Not to be used in organic grows, only chemical grows. Its ok to use it with every watering, you would have to use a large amount to mess the plants up. 2 tablespoons is just enough to get the good effects from it. it will not cause problems in smaller doses.