Where are you in the grow, ie how big is your plant/ plants?
What is your nutrient strength, EC/ppm?
What is the total volume of water your system holds?
Large plants in small volume systems will be more susceptible to pH fluctuations. Lower EC/ppm’s will also see pH swings as there are fewer dissolved solids to buffer the pH.
AN’s pH perfect “technology†is a combination of added dissolved solids and other buffers that stabilize pH. Like other nutrient lines it hinges on the grower using the proper ratios from each bottle, which of course isn’t exactly what they recommend in their marketing material.