Maintaining the right level of oxygen is one of the most important factors in the game. You have several pieces of equipment for the purposes of its production, and for keeping the appropriate composition of air at your base. The first category is the oxygen producing equipment. The first and most used piece is the algae deoxidizer. It requires a lot of algae and electricity. In return, it produces oxygen and some heat. It is also not pleasant to its surroundings, which decreases the value of decor. One upside of this machine, which has to be pointed out, is that it will produce oxygen up to the highest possible concentration in the environment (1800g per field). Do not place it close to any plants, because of heat generation. Over time, you will begin to run out of algae, so you will have to look around for slime and start to extract algae out of it. The second device you must access through research is the electrolyzer, which produces oxygen and a small amount of hydrogen from pure water. It also needs electricity, and you have to supply water to it with pipes. It is worth building it in a large room, so that the hydrogen is gathering at the ceiling and does not poison the duplicates. You can additionally build a pump to pump out the hydrogen from the room into another tank or into a special machine which is producing electricity.
The second category of machines are filter objects. They indirectly produce or affect the level of oxygen in the environment. You will quickly get access to the algae terrarium. It consumes a small amount of algae and some water to convert carbon dioxide (CO2) into pure oxygen! It is a very handy piece of gear, but only in great quantities. Build terrariums where carbon dioxide collects, which is usually at the lowest levels of your base. The ideal situation is to have a water tank close by, so that the duplicates will not have to run a lot. The terrarium has a bonus to efficiency under proper lighting. The air deodorizer is a device that removes contaminated oxygen, passes it through sand and releases a small amount of oxygen and produces a by-product in the form of clay. The big plus is the small size and no need for oxygen. You also have the option to construct an air scrubber. It needs to be connected to a power grid, while also requiring a supply of pure water and CO2 in the environment. As a result, it removes carbon dioxide and produces contaminated water. The advantage of this machine is that there is no loss of water in the process, which can then be purified again using sand in the Water Purifier.