CO2 DIY idea

[Andrew McLeod <thefish at theabyssalplain_freeserve.co.uk>]

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