Silicon is the second most abundant element in the earths crust making up a component of most rocks. Plants absorb silicon from silica that has dissolved into the soil water. As you can imagine the concentration of silicon in soil water is not that high because rocks do not tend to be all that soluble. Silicon concentration in soil water generally does not get above 20 ppm and this is the level we recommend for hydroponic nutrient solutions.
Silicon is a beneficial plant nutrient found in virtually all soils but not, until now, in hydroponic nutrient solutions. Silicon will strengthen plant cell walls and become a barrier against water loss, fungal infection, particularly mildews, and insect and mite attack.
Silicates are very alkaline and care must be taken with its use. Always check the pH after silicon has been added to the tank.