The normal range of silicate in sea water is from 0.0 to about 200 µg. atoms Si per liter at 20° C. It has not been fully demonstrated whether the silicate determined by the method described below is in the colloidal or ionic form or both.
Robinson, Rex J., and Thomas G. Thompson. 1948. "The determination of silicate in sea water." Journal of Marine Research 7, (1). https://elischolar.library.yale.edu/journal_of_marine_research/649