RAPID Si+ is a concentrated form of available liquid Silicate(Monosilicic acid). Monosilicic acid is the only form of silicon that can be absorbed by plants. Nature has a complex and time consuming method of converting microbes to other forms of silicon into monosilicic acid. Once converted to monosilicic acid, rapid absorption is necessary because monosilicic acid is highly unstable and quickly reverts back into non-absorbable silicon.