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Re: Moving from Yeast CO2 to Bottled CO2

I agree with James Purchase that regulating the CO2 content of four tanks
to be used in a substrate experiment would be necessary. The CO2 level is
an important variable that can have a large effect on plant growth.  I did
an experiment years ago where I maintained three different levels of CO2 in
three tanks, and I measured the CO2 content daily with a method similar to
the one used by Jame's LaMotte test kit.   Excluding the very expensive
method of using pH controllers, solenoids, etc., leaves only methods that
are going to require time spent every day, measuring and adjusting CO2
levels.  I have never tried it myself, but, from what I have read on this
mailing list, it seems that attempting to get a steady, low, flow from a
CO2 tank by adjusting a needle valve is too unreliable.  Sooner or later,
usually sooner, something changes.

I was wondering, if glass capillary tubing could be used to regulate the
flow, instead of a needle valve.  This is a thick glass rod with a narrow,
central capillary like the one in a glass thermometer. It comes in a
variety of capillary diameters.  With a little trial and error, it should
be possible to get the diameter that would give you the flow you wanted to
maintain the desired CO2 content in your tank.    It should also be
possible to adjust the flow by changing the length of the capillary tubing,
assuming that the greater friction of a longer tube would reduce the flow.

A glass capillary tube wouldn't be subject to all the problems of
maintaining a constant flow rate with a needle valve.  As long as the
pressure from the tank stays the same and the gas does not have particulate
crud that could clog the capillary, the flow should remain constant.  The
biggest threat from a needle valve is that it could start letting too much
CO2 through and kill your fish.  This could never happen with capillary
tubing, unless the pressure went up, somehow.

I'm probably getting carried away, but capillary tubing could be regarded
as resistors.  Put two in parallel and double the flow.  put two in series
and halve the flow.

Has anybody tried this?

Paul Krombholz, in soggy, central Mississippi, starting on our third rainy