We use GE NT4200 as the corrosion inhibitor in our cooling water systems and we noticed an unexpected trend. pH has been slowly decreasing over the past 6 months (from about 9.5 to 9 on four different 50SGs and from about 10.0 to 9.6 on two 34 SGs). At the same time, the Nitrite concentration has remained constant or has slightly increased due to cooling water makeup.
We expected the opposite – pH should be relatively constant while Nitrite concentration should decrease as it is consumed.
Has anyone else experienced this issue?