Not sure what pH range you are looking for and what is causing the pH change, but here goes. 2 phase aluminum bronze, such as C95800, has good corrosion resistance in acidic enviroments. For instance in 3% HCl at 20C it has a corrosion rate of about 10 mpy. I'm not sure of the pH of that solution, but is has to be low. As pH goes down you also start to worry about dealloying. Aluminum bronze has more issue with higher pH environments of caustic soda which tend to quickly strip the corrosion resistant alumina film.