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CO2 tubing

Neil wrote:

>I have "been told" that conventional air hose is not good for CO2 because
>it will diffuse out.  Supposedly, not true for silicone and some other
>materials. Vinyl also gets brittle with age and this 'may' affect the
>diffusion. Comments or references? 
>Even if true, I now wonder about speed of the diffusion. Maybe it is of no
>practical significance for aquarium applications unless the length of
>tubing is high and the gas residence time is long. For example, if there is
>a 1 percent exchange in 1 hour, we would not care.  

I don't know any exact figures for diffusion, but Claus seemed to think
that for short distance runs, it would not be much of a problem.  If you're
piping it through several different rooms, you might lose more CO2 than you
wanted to pay for.

As far as vinyl becoming brittle is concerned, I just went and checked the
tubing of my first CO2 system, which has been running without interruption
for over 5 years.  The tubing is till very flexible, with no sign of
cracking, discoloration or deterioration.  I think I paid less than $1 for
the length I needed, so I think I got my money's worth, even if it _did_
fail at this point.<g>

Karen Randall
Aquatic Gardeners Association