It looks like we're thinking backwards then. Aeration raises ph based on your last test...possibly by releasing CO2. What about metering CO2 into your water then? I know some use CO2 scrubbers on SW tanks to raise ph. What if you do the opposite and add CO2?
This may sound silly, but we can try a simple test. Fill a glass with water and let it sit for a bit. Check it and see if your ph is high. If so, get a straw handy. Take a breath and exhale through the straw into the water. Do this a few times and check again. If there is any logic to this, the ph should drop. It may be slight, but that's all we're looking for at the moment.
Good luck!