Scale is a deposition of Total Hardness present in water i.e. Calcium Carbonate , Magnesium Sulphate , Silica etc , which dose not allows the heat transfer from the system.
General Corrosion
Corrosion forms due to oxygen present in water in free state , which causes pitting , punture & metal loss.
Pitting
Algae
Bacteria secrete a slime that functions as a binding or cementing agent for dirt & chemical precipitaties , forming on occasion slimy or sticky , coherent masses that obstruct the circulation of water
