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Enclosed ecosphere


Both the lack of oxygen and the accumulation of CO2 can be problematic. Balancing it out with the right amount of plants/algae is likely not easy, especially if you neglect the importance of the air compartment in the ecosystem. With reasonably-sized headspace air, you could create a buffer for oxygen/CO2, but it would still be walking on a tightrope. In the long term, you probably need to either balance CO2 production and consumption or implement regular air changes, similarly to the water changes in aquariums, to reset the system.
I've seen a video on YouTube of a guy who experimented with this and he kept several jars of water from a pool with snails and other critters and monitored its development for some time. I only remember some pond snail in it didn't survive. The rest I've forgotten, but that video is out somewhere, can't find it back in my history it was too long ago... Maybe in a moment of clarity, I'll remember some more and find it back.

Wiki also has an article with references to the Ecosphere aquarium concept.
It seems that it always goes out of equilibrium and multicellular lifeforms will not survive (I guess shrimp and or Daphnia and such) but a number of microorganisms and bacteria will finally establish.
a number of microorganisms and bacteria will finally establish
There are many species. Their life strategies are much more variable than those of multicellular organisms, and can complement each other, creating full cycle. Their life cycles count in hours. So, some kind of microbial assemblage always survives, even thrives.
To produce surplus of ... whatever essential for multicellular organisms is quite different story.
It's quite possible to provide oxygen and carbon without letting air in. Par example, citric acid and iron (III) oxide - an enormous source of oxygen. The caveat is that the microbial community will adjust to that and won't leave anything - par example, oxygen - as it is; more oxygen respiring microbes will develop. At certain level of complexity, fungi and then algae may join the party. But we're still far from creating a system able to sustain higher plants, not to mention crustaceans, etc.
Such studies are interesting and useful for studying, par example, the Earth's past, or for environmental modelling. Unless you've got well-equipped laboratory, though, you'll hardly produce anything more than a bucket of opaque, foul smelling water. (At that moment I'd throw in a silver coin and observe whether the water clarifies...)
I tried this a few years ago, I don't really remember what I did or how long it lasted but I did get some shrimps to reproductive age. I think it did last a while I just cant remember why I no longer have it. I think in a bigger container than I tried it would have lasted a really long time. At 4:55 in this video
Some 3D printed coral later, its done!

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Setup today with some eggs next to my little freshwater planted setup.

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Now wait and see if the eggs hatch, will be feeding them spirulina!