Calcium and magnesium silicate scales are very difficult to remove by chemical means. In some instances hydrofluoric acid or ammonium bifluoride has been used with some success. However, the handling of these materials is extremely dangerous. Alternate acid and alkaline cleanings have also been used to combat this problem. Usually the formation of silicate scales can be prevented by limiting silica levels to approximately 150 ppm in the circulating water, although the precise limits are determined by other system and makeup water parameters. For example, if magnesium is present with sufficiently high concentrations of silica, magnesium silicate can form.

To prevent magnesium silicate deposition, the magnesium and silica concentrations are controlled so that the following solubility product is not exceeded:

Raw S102 (ppm) x Raw Mg (ppm as CaCO3) x (cycles)² -

< 36,000 (ppm) if circulating water pH is 7.5 or below

< 25,000 (ppm) when pH exceeds 7.5

It is important to note that many silica deposits are due to absorption on other precipitates. In general, silica should not be a problem if deposition is controlled and the above guidelines are followed.