another thing to think about re: the pH question is, it's winter time, so your home is probably not getting a lot of fresh air in it. this results in less oxygen in the air, so your tank has less dissolved oxygen, which will cause more dissolved CO2 and a drop in pH. Before dosing, I'd put an airstone in your sump, or run an airline from outside (via a window or somethin) into your protein skimmer air intake.
I'd suspect this phenomenon is a likely culprit in your case, because you haven't seen pH problems before, and it's a slow change.
As for the 'trates, short of having a place for anerobic bacteria to grow, you can't get rid of them without growing macroalgae or water changes. In nature, the bacteria that convert nitrates to nitrogen gas can't do so in oxygen-rich environments, so we don't usually get them in our tanks. I prefer throwing some chaeto in the sump, personally-- seems to remove nitrates pretty well, and I sell a chunk of chaeto to my LFS every month. :) good luck!