Pure ammonia actually has a basic or alkaline pH. So in theory, ammonia should raise the pH of an aquarium. However, virtually all processes in the aquarium that produce ammonia, as well as the breakdown of ammonia produce hydrogen cations. Since pH is the negative log of hydrogen cation concentration, increasing this lowers the pH, negating the mildly basic pH of ammonia. So while ammonia has a basic pH, the processes that create it in an aquarium produce enough hydrogen ions to overcome this and lower the pH.
If you are doing enough water changes in a stocked tank, and have a decent KH coming out of the tap, you won't see a drop in the ph due to biological processes.
Not sure why you want a higher TDS value using old water.