I also use Advanced.. I haven't noticed a creep up in pH, but I don't bother checking the reservoirs after I initially mix and balance. From what you described, you may want to consider only mixing about 5 days worth at a time. This is working well for me because I flush on the weekends and start the cycle over again with fresh water/nutes for the next ~5 days, depending on the uptake .. I use Rubbermade 18 gal cans, and typically fill them to about the 10 gallon level (~40 L), with one dedicated to veg, 1 for each of my 2 groups of flowering plants (since their needs vary..) for a monthly harvest. Very little waste and no issues.

Good luck!

Farmer Rich