I've never had a problem with pH and air. It's nutrients without sufficient "pH buffer" that cause pH swings. Google how a chemical pH buffer system works, it's magic, it's like a chemical control system. Phosphoric acid and Carbonates work well to keep pH in a non-linear zone.
"Surface agitation" is what drives gaseous exchange, research "flooming", it's what they use in aquaculture. It's just churning the surface of the liquid that facilitates gaseous exchange. Like a swelling in the centre. Much quieter and not a waterfall per se, but it works as well. The splashing of water also works, but it not necessary except for wetting above-surface roots I find, like the ones growing out net pots. Hence why I'm drifting back from flooming-waterfalls to having a good bubble spray.
Are you sure your temps are in range, and the water is churning inside the root mat and at the bottom of tote? These issues are why I'm going back to taller buckets with smaller plants than scrog totes, so that they can in-actuality have a current flowing all around and the root-mat. Also I ask myself when I build a system that water may be sufficiently oxygenated on the surface but is it really penetrating and swapping out solution right from the middle of a massive root mat every 5min? It's all about how water flows in rdwc that means healthier root growth.
I have had more problems with bulkheads that grommets, weird.
As the bulkheads you was using was pry junk and probably not the current culture spin tight bulkheads as I haven't had a single leak and I have x4 per tote for drain and water pump...Yes I am sure my temps are correct and using cultured solutions nutes right now...Also like I said even current culture took out their matala disc for their epicenter because of pH problems it was causing in the system as I took mine out and my levels stay stable even at 6 weeks since last res. Change and still fine...So works for me...I'm a true believer in both flooming and waterfall for do over air stones but that's just me however airstones has their place that's for sure as they obviously work...Million ways to skin a cat...I was thinking about power heads in each tote instead of waterfall however I may try it in my new cloner and see how I like it and go from there it would be easier than waterfall manifold and lines but will see efficiency is huge for me since I grow for my own personal use and that is it I'm very selfish like that....Plus with how sick I am it's thee only way period.....Also on the bulkheads makes a big difference on if it's a rectangle or circle tote as like a 5gal bucket I could see the groumets working as I've used small 3/4 grommets for some dwc buckets i used to run that's now for males or a mother if I choose to have one lol...