The Co2 tubing thing got stirred up a little while back and now it seems like everyone is insecure about their tubing *no puns please*.
I don't think it's a cut and dry thing. For example, I would imagine Co2 permeability for silicone would be one value in a high pressure setup, such as a glass diffuser, and quite another value for a low pressure setup.
People have been getting along fine for years just grabbing whatever tubing they could find. I'd be more concerned about my method of diffusion being efficient than the walls of my tubing. Besides, a lot of us are blowing Co2 bubbles all over the place so obviously making use of every precious molecule of Co2 isn't a top priority.
Having said that, if I were running an external reactor, I would use Co2 PROOF tubing because the setup would be permanent and because it would not require the tubing to be highly flexible.
I'm currently running glass diffusers and I'm using the grey ADA tubing on one (could just be silicone, dunno) and regular clear vinyl on the other.
I'm not running long lengths and it's very important to me that the tubing be very soft so that it's easy to connect to glass diffusers and run along the sides of the tank without putting pressure on the glass connection.
Now, I have 40 ft of that black Co2 PROOF tubing that I bought from Rex. I bought it back when I used an external reactor and I switched to glass diffusers before I got around to installing it. It's sitting in a box with other aquarium excess. If anyone wants the stuff I'll sell it.
Do a simple test by submerging a 10' length in your aquarium. Block off one end and apply about 2-4 psi pressure. If there is even a 5% loss you will see it in the form of very small bubbles. If you do not see anything and you are loosing CO2 you have just built the most economical diffuser available to the hobby and you don't have to worry about breaking those glass ends that are on the other products.http://www.barrreport.com/forums/newreply.php?do=newreply&noquote=1&p=8263#
Yes. The PROOF tubing has a thicker wall. It's inner diameter is narrower than the inner diameter of the other tubings. This means it makes a *very* tight fit. I couldn't even push it completely over the connections by hand (I didn't take the time to heat the tubing with hot water) and I still had to use a knife to remove it from the barbs of the check valve. The other tubings just pulled off.
I'm fairly confident if I tried to force the PROOF tubing over the ends of my glass diffusers they would break into a million pieces.