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I believe you would pump in CO2 (and any missing nutrients), not Oxygen. Algae culture requires CO2 and produces Oxygen. It also requires light. https://en.wikipedia.org/wiki/Algaculture#Growing_algae

If you like plants in your fish tank, pumping in CO2 has an amazing effect on them. Far more growth than pumping in air.

There is some nice hardware for achieving it.

Are they actually CO2 concentrators or some variation of buying dry ice or compressed gas and injecting it?

I did it by running gas off fermentation (sugar and water) and it worked amazingly well.

I’d have to refuel about once a week.

Doing via CO2 bottle is the way I’d do it now and is how the impressive displays do it (for the ones I’ve seen).

I should have written air instead of oxygen, though plants still do respirate oxygen even though they’re net positive oxygen producers.