Double check the calibration and blow down point of your T.D.S. meter. When Total Disolved Solids reach 1200-1500 p.p.m. a controller should have energized a blow down solenoid. If the solenoid is malfuntioning or the line is plugged up the solids will continue to build, this not only affects cooling tower capacity but will also foul any heat exchangers in that system. One why to identify a fouled condenser is to look at the approach and the delta t on the water side. High approaches with a small delta t could be an idication that the tubes are fouled. The approach of the cooling tower is also a good way to see how well your tower is rejecting heat. Just a few things to consider.
I'm not a real engineer, but I play one on T.V.
A.J. Gest, York Int.