JKB, the system that I use is not what it appears to be. The blue lay flat hose ends about 12" inside the white PVC. The White PVC acts like a vortex, and O2 is mixed with the well water inside the pipe. I have basically 0 DO in the well water when checked as it comes out of the lay flat hose. By the time it's coming out of the PVC pipe, it's up to 8.50 mg/l.
Didn't notice the white PVC. That's all gravity, or minor pressure thru the blue to the PVC, then it sucks some air toward the end? Makes sense. What do you think the retention time is when the water hit's the PVC?
Unless your well water is heavily laden with the 3 that Cecil mentioned, Hydrogen Sulfide being icky, and CO2 being a prick, It's always a safe bet to blow off some gas. Well water will pick up some DO as soon as it is out of the ground. Blowing gas off makes this happen faster.
247, the 3 bucks was well spent! Also looks cool!