Promix has buffers built into it, which will try to offset the tendency for fertilizers to lower the Ph. I grow in
Promix and I really can't say that I've ever had a Ph problem.... and you are correct in most new growers stumble on Ph and overfeeding. Most tap water is close to neutral in Ph, and shouldn't cause issues and can actually benefit the plants by supplying magnesium and other minerals. The key is "most" tap water, not all. If your Ph is excessively high in your water, you can either filter it (RO), distill it, or lower the Ph. I add wood ashes to help the buffering even more, but that isn't a necessity, just some minor nutrients and buffering to keep Ph in the correct zone (which it does on it's own for the most part). With my use of
Promix, I only feed every two weeks on average, so I don't use a ton of nutrients to lower my Ph too much. Using a lot of nutrients will lower your Ph more than the occasional feeding. A lot depends on your method of growing.