Calgon conditioning is a process used in water treatment to prevent scale and sludge formation in boilers. It involves the addition of Calgon, which is sodium hexametaphosphate, to the boiler water. The added Calgon forms a soluble complex compound with CaSO4, which prevents the formation of scale and sludge in the boiler. The complex formed is soluble, so it does not cause any problem to the boiler. Calgon conditioning is considered better than phosphate conditioning because it forms a soluble complex compound with CaSO4, whereas phosphate conditioning forms insoluble compounds that can cause problems in the boiler.