What ends up happening is a lot of people will set up their process that is close to the edge to qualify the most economical parameters. If you are too close, once acid adds into the bath, that pH may struggle a little bit. As you are getting closer to your bath life end, you may be adding chemistry to increase your cleaning capability. A way to mitigate that is to increase the concentration just slightly or select a cleaning chemistry that is not as affected by the pH.