Humboldt Nutrients S.I. Structural Integrity QuartS.I.'s proprietary blend is the most advanced silicate additive on the market today; formulated to instantly supply your root zone with the silicate needed to build strong, thick cell walls and cellular membranes, thus giving your plants the ability to hold heavier fruits and flowers. With S.I. from Humboldt Nutrients, your plants will have the building materials they need to create the superior plant structure needed for driving a large and robust harvest.