"The pH of marine aquarium water is intimately tied to the amount of carbon dioxide dissolved in the water. It is also tied to the alkalinity. In fact, if water is fully aerated (that is, it is in full equilibrium with normal air) then the pH is exactly determined by the carbonate alkalinity The higher the alkalinity, the higher the pH, and equilibrated with air having
extra carbon dioxide as might be present in a home (1000 ppm). Clearly, the pH is lower at any given alkalinity when the carbon dioxide is raised. It is this excess carbon dioxide that leads to most low pH problems for reef aquarists"
That was a quote from one of Randy Holmes articles. With fresh o2 in the house it could affect the ph in our aquarium , also if your refugium has seen good growth over the last bit, it could also take up amount of co2 in the tank and by reducing co2 level we know it will also raise ph. Just food for thought.