Abstract: A system is provided for controlling a rate at which a treatment fluid is introduced into a main stream to be treated so that a selected characteristic of the main stream matches a set point for the selected characteristic. A pilot stream is diverted from the main stream. The pilot stream is treated with a known amount of the treatment fluid and is analyzed to determine if the selected characteristic matches the set point for the selected characteristic. If the set point for the selected characteristic is matched in the pilot stream, a related amount of treatment fluid is introduced into the main stream. If analysis of the pilot stream indicates that the level of the selected characteristic is above or below the set point, the rate at which the treatment fluid is injected into the pilot stream and the main stream is appropriately adjusted to cause the selected characteristic in the pilot stream and the main stream to more closely match the set point for the selected characteristic.