What's the TA, CH, and pH of your fill water?
This is the driving factor for your pool over time, specifically TA. The well water at my house is TA of 260, so I'm constantly adding acid to keep pH down. With a pool your size, you might consider an acid injection system to automate this process. You also might consider adding another SWG cell to prevent needing to manually dose a SWG pool just to keep the water safe.
Does your pool have in floor cleaners? You'll need to set up with programming (I'm a pentair pool owner so no help there, sorry) to make sure the spa water gets circulated some and chlorinated throughout the day when not in use. The good news is with a spillway (and other features like fountains and waterfalls) you are able to drop the pH to 7.4 or 7.2 and relatively quickly "aerate" to neutralize TA. The lower your TA gets, the less acid it'll take to keep your pH at the desired number.
Not sure how that influences the oxygenation ongoing with the spa waterfall.
The relationship between TA and pH doesn't exactly work like that, but it's not critical to understand more than "TA causes pH to rise over time, making the water change from more acidic to more basic (low pH to high). Temperature, splashing, wind, swimmers, bubbles, and rain all speed up the process." It's been a few months since I internalized this and I'm sure I've gotten a few of these details incorrect, but basically:
Try to think about it like a can of soda... Oh wait, we're both from Texas... Think about it like a can of coke. When I add muriatic acid to my pool, it makes the water lower in pH (more acidic). The strong hydrogen ions in the muriatic acid attract the carbonate ions in the TA away from the weak calcium and sodium bonds, and some of the muriatic acid in my pool has now been converted to carbonic acid.
That's a very nerdy way to say, some of the acidity in my pool is now carbon dioxide, just like in a can of coke, and bubbles form, float, and pop. The offgassing of CO2 has a buffering effect by releasing the acidity of the muriatic acid slowly over time via the carbonate alkalinity in the pool. That's why TA chemicals are often called "buffer" and the most common chemical for this is baking soda... Sodium bicarbonate.
Aeration, turbulence, bubbles from the SWG only speed up the carbon dioxide offgassing process, just like shaking up a can or bottle of anything fizzy. It's not about about adding oxygen or anything else to your pool water, the carbon is already dissolved in your pool. It's just happy being weakly attracted to sodium and calcium until the super attractive hydrogen comes along and yanks it away.
Or, if you prefer, this meme.
