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RE: DIY CO2 reliability

Someone said:

"Ryan, for the cost of a "good" pH meter, you would be able to get a
perfectly sound CO2 regulator and pressurised gas system. You can forget
about ever being able to reliably hit a specific pH with a DIY yeast
reactor. The output is too variable."


I recently started to play with DIY CO2 &, after a number of attempts to
build reliable CO2 reactors I settled on the following approach which
maintains the tank CO2 at a level independent of the amount of CO2 gas being
produced by the fermenter.

Find a box of some kind that has a clear plastic lid (so you can see the
water level in it when it's submerged) in the form of an 'enclosure' (i.e.
when it's upside down, submerged in the tank, you can bubble CO2 up into
it).  See below for dimension info.

Keep the lid & discard the box!

Drill a couple of holes in the top of the lid so that you can push some soft
plastic suckers through & still get a gas tight seal as below (sorry of your
font screws up the diagram):

      \        /                                     \         /
       \------/                                       \-------/
 I                                                                  I
 I                                                                  I

Stick it under the cover glass so that the underside of the box is below the
water surface & in a position such that the outflow from the filter (or a
powerhead) flows past it (my tank has a glass 'lip' that runs all around the
edges so I put it under that, at the back).

Run an airline from the CO2 fermenter under the water, along the back of the
tank, & arrange for the CO2 to bubble up into the box (when you submerge the
box for the first time let all of the air escape so that its just full of

Use a fermenter that significantly oversupplies CO2 (I use 2 x 1 gallon
glass 'demijohns', available cheaply in the UK for home winemaking, joined
with an airline 'T' piece.  I change each one every 4 - 5 weeks but around 2
- 3 weeks apart so that there is always a very active fermenter running).
Once the box is full of CO2 any additional CO2 overflows (underflows?) &
escapes as gas at the surface.  The CO2 content of the tank water is
determined only by the submerged surface area of the box, the rate of water
flow past the underside box & the rate at which CO2 escapes from the tank
elsewhere due to surface agitation, air-stones etc.  It's unrelated to the
rate at which the fermenter produces CO2 (providing that you are always

Initially I tried the lid off a box of emergency auto bulbs that I had in
the garage (about 14cm x 9cm) - this gave about 45ppm CO2 in my 55g tank
(next to the venturi outflow of a Fluval 404).  I then tried the lid off a
box of push pins (about 7cm x 6cm) this gave about 10ppm.  Finally I settled
with the lid off the box containing a $2 'Paper-Mate' biro (about 17cm x
4cm) which gives about 18ppm.

Hope this is useful!

Regards, Kevin