CO2 -vs- Plastic

[AquaVelva]

I have a couple of questions about the effects that CO2 has on plastic. Both these questions have come about after reading various posts and articles about CO2 injection.

First, does CO2 somehow cause plastics, such as filter impellers, to break down? Seems that I have read that injecting CO2 into the intake of a filter is a bad idea because it is hard on the impeller in some way. But it seems like such an easy way to dispurse CO2 into your tank!

Second, can CO2 actually pass through standard vinyl aquarium tubing? This would not seem possible to me, but I know I have read where you experience great losses of CO2 when running it through vinyl tubing. Some people say to use silicone tubing or special CO2 resistant tubing. How come?

Can any experts out there clarify this for me? I hope this is not the wrong forum to post these question to, but the "plant people" are the ones with the CO2 experience.

...AV

[superjohnny]

Lemme take a shot at this...

I have no experience with CO2 causing plastics to break down. That said I don't have very much experience with CO2 so maybe it's just lack of experience. The only way I can see to harm your canister filter by using it to diffuse the CO2 is by burning out the impeller motor from it cavitating. It's meant to push water, not air. I don't have any experience with burnt out impellers, but from time to time when I push too much CO2 into my canister it will cavitate (this is also called getting "air locked"). Basically, the pump stops pushing water because there's too much air in the canister and it loses it's siphon.

Ok #2, CO2 can pass through "normal" air-line tubing. Silicone tubing is less porous and therefore does not allow the CO2 to bleed out. To use an analogy, regular air-line tubing is like using a chicken-wire fence to keep out water. Water molecules are small enough to (easily) fit through it.

Don't take it as fact, it's just my experience. ;)