Sam,
No, that's not an option for three tanks, and all tanks suffer from low pH because of the excess CO2 in the house. I even feel kind of sluggish after a night's sleep, so the CO2 is not only affecting the tanks.
What we set up tonight to try to decrease CO2 and increase O2 overall, is open the two bedroom windows a bit, one facing east, the other south. Then we pulled an ocellating fan out of storage and set it up outside both bedrooms with the air being pushed into the living/dining areas where the tanks are. Am going to experiment with this for awhile, while it is still relatively warm
DH is going to ask the building maintenance people at work (in one of the Telus Towers) what they might suggest. Will report any positive results.