I’ve never run across your posts on here but this is the second time today I’ve encountered you dropping chemistry knowledge,
You must not read the chemistry forum much. I run this forum and respond to most threads in it. With my 38,700 posts, you cannot read much here and not run into me (for better for worse).
I was reading through this and while I can’t quite find why exactly the OP is looking to raise pH in this manner, I disagree with your last statement that running O2 through the water will lower the CO2 or N2 in the water. I forget the name but there is a law or theory out there that points to solubility of CO2 vs. the other diatomic elements in our atmosphere. CO2 is far more soluable. However, this same law/theory shows that when you take normal atmospheric air and place it in contact with aquarium water, it will drive towards equilibrium which will pull O2 in and drive out N2 and CO2. This is also a similar method used in fishery systems but they use pure O2. There is also a similar method used and I’ve heard of them being called stripping towers, where they use normal air. Not sure if that’s the industry term though. But either way, if you force air that is empty of CO2 through water, it will help to drive out the CO2. They key is making it free of CO2. Maybe I just said what you did, but it seemed like you were saying the addition of O2 has no effect on CO2 and I don’t believe that be the case.
I'm certain I did not mention N2 in this thread at all. Are you referring to a different thread?
You are probably referring in general to Roults law or a variant of it:
en.wikipedia.org
.
There are many complications to using such laws to apply to our reef tanks. The most important of which is that the tank is often not at equilibrium with the air around it. If it were, there would be ZERO pH change day to night. Since almost no reef tank has zero pH change (due to photosynthesis consuming CO2 and respiration adding CO2), the water is not at equilibrium with the air.
But, to expand specifically on the relationship between O2 and CO2...
Many processes we use impact only one and not the other, thus, the simple thought that photosynthesis consumes CO2 and makes O2, and respiration consumes O2 and makes CO2 are not the only game in town. Maybe not even the most important ones in a reef tank. So they do not move in tandem.
Let me give some hypothetical examples that show how these processes might impact a reef tank:
1. I carefully bubble pure 100% O2 into a reef tank. The bubbles all dissolve fully before reaching the top and popping. That clearly adds O2 to the water and has no impact on CO2 or pH.
2. I carefully bubble pure 100% O2 into a reef tank. The bubbles partly dissolve fully before reaching the top and and then pop at the top. That clearly adds O2 to the water and will remove some CO2 that entered the bubble that was extremely low in CO2 to begin with. By Roult's Law, CO2 entered that bubble to bring it toward equilibrium with the water, and when it popped at the surface, that CO2 was released to the air. Thus, CO2 in the water was lowered, and the pH rose.
3. This is #2, but with N2, not O2. I carefully bubble pure 100% N2 into a reef tank. The bubbles partly dissolve fully before reaching the top and and then pop at the top. That clearly adds N2 to the water and will remove some CO2 that entered the bubble that was extremely low in CO2 to begin with. By Roult's Law, CO2 entered that bubble to bring it toward equilibrium with the water, and when it popped at the surface, that CO2 was released to the air. Thus, CO2 in the water was lowered, and the pH rose. By the same process, O2 entered that bubble to bring it toward equilibrium with the water, and when it popped at the surface, that O2 was released to the air. Thus, O2 is lowered and pH rises.
4. This is #1, but with CO2, not O2. I carefully bubble pure 100% CO2 into a reef tank. The bubbles all dissolve fully before reaching the top and popping. That clearly adds CO2 to the water and lowers pH. It has no impact on O2. Thus, CO2 rises, pH falls, and O2 remains the same.
5. I carefully bubble pure 100% normal outside air into a reef tank. The bubbles partly dissolve fully before reaching the top and and then pop at the top. This is the example of a person running outside air into a skimmer. O2 CO2, and N2 all move toward equilibration with the gas in the bubble (normal air). Whether each of those enters or leaves the bubble depends entirely on whether the water is supersaturated or undersaturated with respect to that air bubble. What exactly happens will vary greatly between reef tanks and between times of the day on a given reef tank.
Bonus section...
There is a huge complexity that is typically ignored by even chemists discussing such issues in reef tanks, and that is the pressure inside the bubble. A bubble below the surface is under more pressure than at the tank top. That pressure tends to drive all gases into the water, more so than the same air at the tank surface. Thus, air bubbles driven deep into aquarium water will tend to drive up O2, CO2 (lowering pH) and N2 compared to that same air aerating at the tank surface. This is complex to model and understand because bubbles move rapidly between different pressure zones, and equilibration of gas is a slow process, not an instantaneous one.