You dont need injection then, and it is correct that air injection can increase pH by bubbling away CO2 cum nitric acid from the water.
To make it even more interesting, air injection can also lower the pH depending on the starting conditions.
Unless one is really on top of water chemistry, better never use air injection, whether through a stone, membrane, whatever, in a reservoir that is not continously monitored and adjusted as necessary...... The circulation pump will increase the oxygen content of the water through agitated surface exchange and is just as efficient.
Virtually all oxygen absorption happens at the surface level, so if you can direct the flow from the pump outlet in such a way it agitates the surface.... Bobs ya uncle!