Would yours then be roughly 24 mg/liter with 8 being normal?
It depends what you are measuring. Not sure if you have seen my setup but I have 4 res feeding 4 internal res and they sit in 4 totes.
Totes hold the O2 rich air. O2 is injected at the internal res where the fogger is.
Add to that I keep making changes to the system that impact the readings.
So as a general response I would say that the appropriate measurement for this purpose is the one Aqua gave you. But clearly there is more to it than that, and I am still learning about all this with this grow.
To respond to your DO question, using the OG can in fact raise 70 Gal of water sealed up to more than 24. If compressed, significantly more.