Boiler water treatment- What ph level to maintain??

Boiler water should be always alkaline, as acidic medium accelerates corrosion. only in a alkaline environment, steel will stay as steel in contact with water. Steel and water in touch is like petrol and matchbox together. Always they have huge affinity to each other. Acidic environment just lights the fire and ur boiler inside will start rusting, giving dark brown water when u take samples for tests.

Boiler water should be treated to a ph level of 9.5-11.5 as UNITOR, a big player in boiler treatment chemical market, recommends. 

Alkalinity is normally maintained by adding sodium hydroxide, branded by different chemical companies in different names. UNITOR brands it as autotreat, VECOM brands it as BOILER TREAT, and so on...

Sodium hydroxide provides a highly alkaline environment in the boiler. This is about the only environment where water and steel get along well. Heat magnifies the normally corrosive effect water has on steel, since it speeds up chemical reactions. Maintaining the correct alkalinity range minimizes this highly corrosive effect of water. Alkalinity also plays a critical part in various chemical reactions in the boiler. Frequently, most of boiler water alkalinity comes from the addition of sodium hydroxide in the chemical program. Some of the alkalinity comes from naturally occurring alkalinity found in raw water supplies. If it is present naturally, it contributes to the required alkalinity in the boiler and decreases the amount of sodium hydroxide needed.