Just a cheap flowmeter but saying that I only have enough flow to have bubbles just breaking the surface. Any more gas is wasted
A flow meter is a good thing to have otherwise its kinds like shooting in the dark with how much oxygen you are adding. We do have these flow meters but perhaps we should make this flow meter part of the oxygen kit bundle.
If you are using a pressure fermenter then you can do something like this which is what I have built:
This means you can have a closed fermenter and you might have a better idea what you are dosing into the fermenter if you can at least limit what you are blowing off. Also when the fermenter is under pressure it should theoretically absorb the oxygen a better.
If you had very accurate scales you could also weight the gas cylinder but the weight difference will only be a couple grams so potentially difficult to measure unless you have some fairly good scales and even small things like the pressure applied with the hose bending as you move would need to be isolated from the cylinder weight.