This is my answer to some people who previously asked essentially the same thing:
Some companies try to pull a fast one on us. 'monosilicic acid' (a.k.a. orthosilicic acid) is just the form soluble Si takes when hydrated (dissolved in water) at acidic pH. At more alkaline pH (starting around 8.5 ) Si becomes ionized, but at pH <8 Si takes the form of monosilicic acid in solution, which is the form plants uptake Si, and then they convert it to SiO2. Its basically a fancy way of saying 'watered down silica' and allows for the company to list a higher % on the product than if they expressed the % in just Si, so the product appears to be more concentrated but it isn't. As pH increases above 8.5, the Si in solutions changes to ionized polysilicic acids, at 9.3-9.5 disilicic acid stabilizes, at pH below 4 non-ionic polysilicic acids form. But as long as you keep pH 4<8 more than 99% of your Si will be in the form of monosilicic acid.
silicate salts are highly alkaline. when added to solution they raise the solutions pH. As pH raises to greater than 8 (>8), the form that silica takes in water changes from non reactive, non-ionic monosilicic acid, to reactive, ionic polysilicic acids that react with other minerals (unsure of which ones) and precipitate out of solution, giving a cloudy appearance.
Basically at high pH (>8) silica changes forms to a form that can react with other minerals and precipitate out of solution. The best way to prevent this is to add your silicate salt first out of all nutrients, and then lower the pH (add acid) to levels that will insure that pH wont rise to >8 when adding your other nutrients