Tamer, Calcium carbonate ...

Tamer,

Calcium carbonate and calcium sulfate scale is typically prevented by utilizing dispersant polymer technologies. These are typically acrylamide based polymers with differing functional groups. The type and amount of these dispersants required is dependent upon your calcium, alkalinity, and sulfur concentrations, pH, and temperature experienced within the system.

In my experience, citric acid is utilized most effectively to chelate and clean iron scaling, however, it can be used for cleaning of calcium carbonate and sulfate scales.

Unless something has been brought to market recently, I do not know of anything that will remove or prevent scaling of silica. This is typically done by limiting the silica concentration of your water and increasing the pH. Pretreatment of the water utilizing some form of lime softening will also help to reduce the amount of silica to a point.