One little thing I noted: You said you are using a Taylor DPD test kit. I strongly recommend you either upgrade to a Taylor FAS-DPD test kit, K-2006 or K-2006C, or get the single Taylor FAS-DPD test, the K-1515-A or K-1515-C, and use THAT instead of the DPD test. It will measure Free Chlorine and Combined Chloramine levels all the way up to 50ppm and down to the .5 level.

Carl