Hair algae (I need help!)

[plantbrain]

A question:
Are oxygen and Co2 levels inversly proportional? I used to think that they were but as of late I am begining to see that they are not?

Not in a planted tank, they are independent of one another.
Remember this.

Is it possible to have certain levels of oxygen in the presence of elevated Co2? I would think the very thing that cause oxygenation would displace the Co2 - but in a condition where the Co2 is being replaced faster than displaced an equilibrium could be achieved? Is there any substance to this idea or is this nonsensical rambling?
I just want to undersand the principle at work here. (if possible)

Well you can have high O2 and CO2 during most of the day, most folks do, both are above 100% saturation(higher % than the surrounding ambient air).

At night, there's generally less CO2 being added(I don't add any at night) and the O2 is now being used up and typically dips below 100% near morning.

We add CO2 to help the plants grow faster, they split water to run the light reactions, not CO2 (CO2 is reduced in separate reaction in the Calvin cycle) and the by product for the water splitting is O2.

The CO2 is used to make sugars, eg the hexose glucose C6H12O6.

Regards,
Tom Barr