You know, it hasn't been an issue, but I've been keeping my fish room open to the 'fresh' air in the garage (never used for parking) during the day time. However, once summer hits and the A/C is on all the time, the numbers may drop.
I changed the way I'm running my calcium reactor, so there is a chance that the increased effluent is adding more alkalinity to the water. I used to drip effleunt, but now it is a steady trickle/flow. Higher alk means higher pH. As of right now, the pH is 8.19 in my reef, and the lights turn off in about 1.5 hours.