I've never used AN, but what I know is.. pH Perfect does the pH almost instantly. There is a video on youtube demonstrating.
But, if you're filtering your water, and it comes out at 0 ppm, them it must be reverse osmosis, right? as its by this process all salt molecules are removed, giving you 0 ppm. When using RO water, or this equivalent of it, you absolutely have to buffer the water with very small quantities of cal mag (50ppm I think?) and make sure it mixes well, cal mag doesn't mix easy. Then pH becomes much much stabler as you add nutes.
But, against this argument, I was under the impression AN pH Perfect preferred RO water, but not sure...
[video=youtube;ElpsVkIHPUc]http://www.youtube.com/watch?v=ElpsVkIHPUc[/video]