In my writeup of oxygenation, I screwed up some of my basic chemistry. A mole of O2 masses 32 grams, not 16 as I used. That will halve the times listed: To get one ppm of oxygen in 20 liters (five gallons plus about a quart) at a flow rate of 1/32 liters per minute, you’ll need half of 1.2 minutes, or about 0.6 minutes of oxygen flow. Round up to account for inefficiency and you can just about say 1 minute per ppm desired. For 8 ppm, use about 8 minutes.
It’s been 40 years since high school chemistry. I apologize for the error.