Check the listing for details. Plant Science Concepts Osa 28 Silicic Acid 4oz, 8oz, 16oz, 1L. Condition: New. Listed at 44.95 USD. Price is for (1) Osa 28 (4oz, 8oz, 16oz, OR 1L) *Please double check selection before paying* OSA/28 plant-available silicon (as monosilicic acid) strengthens cell walls, increases nutrient uptake, and helps plants handle all kinds of stresses. Other silicates are not bioavailable and take time+microbes to become plant available. This makes OSA/28 the fastest option for delivering silicon directly into the plant cell walls! Silicon also has a synergy with calcium in building better plant structure. Many growers see increased calcium response when feeding with OSA/28.Indoor growing supplements like OSA/28 are manufactured by Plant Science Concepts’ staff of Ph.D. chemists in the USA using domestically sourced ingredients.Indoor Growing Supplement Usage Rates:Root drench: Mix 0.5ml per gallon of water every feeding from early vegetative through mid-bloom Foliar spray: Mix 4-8ml per gallon of water 1-2 times per week