CO2 Raise pH?

I have a 35 gallon reservoir for my 4x4 flood table (using R/O water @3PPM with the Lucas Formula).

pH starts at 5.6 after I've nuted my R/O water (no pH down necessary).

Every day, the pH has been rising a couple of points, and I add some down to get it back to 5.6 (not a biggie).

I flood often enough (every two hours) that the air pump/stones are not necessary, IMO, but I added it "just because".

Anyhow, was just wondering if the fact that I have an air pump connected to two airstones in my reservoir could be assisting in the pH increase. The reason I'm asking is because the CO2 in the tent is constant at 1500PPM, and from what I understand, CO2 in water raises the pH.

Anyone have any insight into this?

Thanks very much in advance for your time.

Bump.

I know we're all rushing to take down all incriminating photos today, but whilst deleting said photos, could someone help me out with this?

Would really appreciate it.

Influence of carbon dioxide on alkalinity
Carbon dioxide can change the pH of water. This is how it works:

Carbon dioxide dissolves slightly in water to form a weak acid called carbonic acid, H2CO3, according to the following reaction:
CO2 + H2O --> H2CO3

After that, carbonic acid reacts slightly and reversibly in water to form a hydronium cation, H3O+, and the bicarbonate ion, HCO3-, according to the following reaction:
H2CO3 + H2O --> HCO3- + H3O+

This chemical behaviour explains why water, which normally has a neutral pH of 7 has an acidic pH of approximately 5.5 when it has been exposed to air.