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CO2 DIY idea

I have had a cunning plan...
DIY CO2 systems produce CO2 by anaerobic fermentation of sugars into carbon dioxide and alcohol (and possibly water). Most use a 2 litre bottle or similiar, using a fixed set of ingredients that lasts for about 30 days, and can be scaled up reasonably to about 50 gallon aquariums.
However, why don't people a mechanism such as a 14 day automatic fish feeder, that, once slowed down to deliver sugar and trace nutrients to a yeast mixture inside a small 'bioreactor' once or twice a month? If delivering food to the yeast twice a month, with 24 doses the mixture could last an entire year! The reactor would have to be fitted with a drain to allow alcohol to be drained from the mixture, and water added, but such a system could provide a relatively steady production of CO2, and if the reactor is immersed in water, then that water heated with a cheap aquarium heater to about 18-25 C (or even higher for greater CO2 production), then the heater could be switched off at night by a simple timer plug to reduce CO2 production at night, when plants are not photosynthesising, but in a less dramatic way than switching off a manual CO2 injection system.
Alternatively, for an anaerobic system, it should be possible to make a food slot that is airtight like an airlock, as oxygen getting into an anaeobic yeast system prevents an increase in gas pressure until the oxygen is used.

Another (potentially) cunning plan...
Yeast in aerobic conditions, like most life, reacts sugar+oxygen--
CO2+water, which would actually be preferable as alcohol poisons yeast,
and since alcohol is not entirely oxidised, the aerobic reaction produces significantly more CO2. However, it does not result in an increase in gas pressure, so it would only produce a CO2 enriched atmosphere, and not produce a flow of CO2 like an anaerobic reactor, but since (I am assuming) CO2 is more soluble than O2, a flow of water through the reactor or an air pump pumping very slowly from the reactor into a diffuser might allow CO2 enrichment.

If anaerobic fermentation was required, and too much oxygen was getting into the system, then a clever systems of 'taps' should allow system pressure to be built up and 'purge' the food slot.

Glucose (simplest sugar) = C6H12O6 (six carbons, twelve hydrogens, six oxygens)
(anaerobic) C6H12O6 --> 2(C2H5OH) + 2(CO2)
Increase in gas pressure
(aerobic) C6H12O6 + 6(O2) --> 6(CO2) + 6(H2O)
No change in gas pressure
The aerobic reaction produces 3 times the volume of CO2 than the anaerobic reaction, but there is no change in pressure.

Andrew McLeod
thefish at theabyssalplain_freeserve.co.uk