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Silicone tubing and CO2

On Sat, 18 Nov 2000 at 16:26:31 EST, Dave Grim <Dgrim62 at cs_com> asked: 

> Can anyone give me information about using silicone tubing (100%) to deliver 
> CO2 to the tank? My main concern is wether or not the gas will make the 
> tubing brittle over time, or if there is a significant loss factor thru the 
> tubing (gas permeability)? Thanks for any help.

Jean-Paul Chicheret has written an article, dated Jan. 7, 2000, in which he
encourages us all to change our silicone tubing, which he says is far too 
permeable ("up to 30%"), for Tygon-brand tubing.  The article can be found 
at http://optimal.free.fr/jpc/articles/tygon_01.htm.  Since it's in French, I've 
hacked out a rough translation below:   


"The best way to deliver CO2

"Between the regulator, which is attached to a bottle of carbon dioxide, and the 
reactor or membrane diffuser, manufacturers of aquarium equipment generally 
supply us with silicone tubing.  However, this kind of tubing is highly permeable 
to CO2.  This becomes increasingly worrying as the tubing gets longer.

"What happens?

"Part of the CO2 which is passing through the silicone tube crosses the wall of 
the tubing, and enters the air.  Tests have recently shown that this can cause the 
loss of up to 30% of the precious gas.  I and a partner in the pharmaceuticals 
industry have run tests on no fewer than 10 kinds of tubing.  As you might have 
guessed, silicone tubing turned out to be the most permeable of all, that is, the 
tubing which allowed the most gas to escape.

"A solution to the problem?

"Yes, there is a solution!  The American company Cole-Parmer manufactures and 
distributes tubing made of TYGONŽ, which does not allow CO2 to get through.  
It is affordable, unlike the silicone tubing typically found in pet stores.  Its 
reference number is R-3603.  Being flexible, it is well-adapted to our 
installations.  TYGON tubing exists in many interior and exterior diameters.  It is 
not necessary to buy the thickest tubing available, but a thickness of 0.8 mm is a 
reasonable minimum.  Obviously, the thicker the tubing, the more resistant it will 
be as time passes.

"I would encourage all users of CO2 systems to change their silicone tubing for  
TYGONŽ tubing from Cole-Parmer.  This will result in substantial savings of 
this precious gas, as well as a better functioning system.  It's nonsense to mix in 
air with the CO2 and water in the reactor.

"I have now observed much better dissolution of CO2 in my Dupla S reactor.  
Air had regularly been mixing in with the CO2, causing some useless free space 
to be left over in the upper part of the reactor.  Since I have been using the 
TYGON tubing, the CO2 is practically all dissolved.  I have observed that the 
efficiency of the reactor, which is already quite impressive, is now even 


Please note:  I'm playing journalist and translator here.  I don't know anything 
about tubing (silicone or Tygon or otherwise), nor do I know anything about 
Chicheret.  I've tried to keep my translation fairly close to the original, 
even when the French sounded odd (e.g. the reference to "precious" CO2).

David (B.)