I suggest consulting the supplier of your heat transfer medium (TEG) regarding the maximum permissible chloride level for this application. A quick survey of various glycol-based heat transfer media suppliers' literature suggests that chloride levels should be kept below 25 ppm. The pH range you are operating at is good for minimizing corrosion in carbon steel so this is working in your favor. You should also be sure that you are using an inhibited glycol whenever glycols are used in a heat transfer application.