https://www.ebay.com/itm/5V-Oxygen-Sens ... SwaW1d6L1z
It is easy to connect to an arduino and gives every second a measurement from 21 to 100% O2 and flow from 0 to 10 l/min
I hope this is useful info because without measuring your yield its just guessing , the only way to check if there is more than 21% oxygen is with the glowing woodstick, which i used first.
The chemical O2 measuring cells are expensive and have a short life span.
Sorry for taking so long to respond:) This is indeed interesting, we have also thought about more inexpensive ways of quantifying O2. We are testing currently the use of oxygen sensors as used in cars to determine the oxygen content in the exhaust. The glowing woodstick is awesome too, bringing back memories from high school chemistry classes:)