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DIY CO2 comments

Some feedback from recent discussions.  FWIW, YMMV, etc, etc.

Recipe and methods:

A while back we had a couple posts from some knowledgable folks about the 
life cycle of yeast and how to better culture them.  I read those posts 
with interest, and made a couple changes to my methods:

   1)  I cut the yeast down to 1/2 tsp/per 2 liter batch
   2)  I aerate the solution for 1-2 hours after addition of the yeast 

The first change was because I figured the 1 tsp/per 2 liter batch
probably exceeded the holding capacity of the solution, the second change
was to extend the aerobic part of the yeast's life cycle.  I dissolve the
sugar in boiling water (mostly to make sure things are reasonably sterile)
then allow the solution to cool before adding yeast.  Aerating the batch 
before adding the yeast also shortens the cool-down time. 

I've had excellent performance from the 4 batches I've made this way.  In
my first trial I went light on the sugar and the batch only lasted three
weeks before it clarified.  At that point the solution was very 'dry'. 
All my earlier batches ('least the ones I tasted) were still pretty sweet 
when things fizzled out. 

The second batch was made with the normal amount of sugar and its been 
running now for almost 2 months.  Its production dropped enough after 1 
month that I took it off the aquarium and just ran the rest into a (mostly 
enclosed) paludarium.  What little CO2 it is still producing isn't going to 

The last two batches are now 4 and 5 weeks old and are both still
producing at about 75% of their peak rate.  Previously the production
would drop off noticably after about 2 weeks and at 1 month would be at
about half its peak output. 


A number of people have mentioned finding leaks in their DIY CO2 systems -
some of them appearing after the systems were built.  I've found that
making the outlet from the 2-liter soda-bottle reactor through the lid
invites problems.  The lid and that potentially delicate seal are twisted
and maniputed each time the batch is changed.  It seems better to put the
outlet down on the 'shoulder' of the bottle - there it doesn't take quite
as much abuse. 


A few weeks ago I posted, asking how to get a DIY CO2 system to produce a 
regular stream of small bubbles.  My thanks to those who responded.  I 
used those responses and some physics to get what I wanted.  Here's what 
I did:

	1)  Reduced the headspace in the yeast reactor.
	2)  Made a very fine nozzle from a styrene tube
	3)  Placed a valve on the CO2 line just above the water line.

Forming a gas bubble at the outlet requires a certain amount of extra
pressure because of the surface tension on the bubble - the smaller the
bubble the more extra pressure is required.  Once the bubble is formed and
breaks away from the outlet the sudden drop in pressure allows the CO2 to
expand and a little 'belch' of CO2 is released all at once.  The size of
the belch depends on the amount of gas in the system and on the size of
the outlet.  Using more solution to reduce the headspace in the reactor
and shortening the tubing (if possible) gives a smaller burst of gas and
makes things more controllable.  Using a large outlet also reduces this
effect, but then you get big bubbles. 

Bill Cwirla suggested heating hard plastic airline and bending it or
stretching it to get a restricted opening.  I tried that, but didn't get
real good results.  I got a better result by using white styrene tubing
(used for architectural modelling -- get it at hobby shops).  I treated it
the way we used to make droppers and pipets -- heated a piece of it and
slowly stretched it to get a thin section of tube.  I cut that at its
thinnest point to get two nozzles with a small opening - about 1/32 inch. 
That gave me smaller bubbles, but instead of a regular stream of bubbles I
still got a small belch of CO2 out of the reactor each time a bubble was

I figured I needed something that would allow a regular stream of gas 
through, but would shut down any bursts.  I experimented with a few 
things, including very thin tubes, small orifices and porous stones, but 
I didn't get anything that worked as well as I wanted.  Whatever 
restriction I used had to be more restricting than the nozzle itself.  It 
was fairly easy to get a regular stream of large bubbles, but a stream of 
small bubbles was tough.

Luvskribs said he (gender assumed) used a gang valve to regulate flow -
something I didn't want to do because I figured a valve would only
increase the pressure and increase leakage.  It also raises the
possibility that someone would shut the valve entirely, leading to a
sticky disaster.  But I broke down and placed an in-line valve for
drip irrigation systems on the CO2 line just above the water line.  That
let me do fine adjustments so I could get the regular stream I was looking
for.  A needle valve probably would work better.  Hopefully I'm not losing
too much CO2 because of the extra pressure.

So now I have what I wanted - a regular stream of small bubbles.  It gives
me a better handle on the flow rate from the reactor.  Also, because the
bubbles are small there is almost no noise when they are released or when
they hit the impeller in a power filter or power head.  The regular bubble
steam also means that the mist of CO2 bubbles coming out of a power head
is fine and regular instead of the occasional hard-to-overlook cloud I 
get without regulating the flow. 

Roger Miller

In Albuquerque, where the rains have passed, autumn approaches and all 
is right with the world.