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Re: CO2 Runs
Our pressurized system is currently supplying two tanks (45 gal & 30 gal) and one pond (about 300 gal). The CO2 tank is inside the house next to the 45 gal. The tubing goes from there via a brass tee to the 30 gal., about 20' away, then to the pond via another brass tee, about 10' away. I'm using 1/8" ID, 1/4" OD polyurethane-ether tubing as recommended by Nalge tech support for CO2 for minimal CO2 loss (the same company that makes Nalgene bottles). The output pressure from the regulator is set at 15 PSI, and I can get way more than enough CO2 at the end of the tubing run. We have our metering valves located right next to each diffuser, rather than at the CO2 tank, so we have the advantage of having higher pressure on the long runs (kind of like how electric utilities distribute electricity with higher voltages to minimize the effect of losses).
The polyurethane-ether tubing was also recommended for use with aqueous solutions, but if you won't be submerging the tubing, the polyurethane-ester tubing has even less permeability to CO2, according to Nalge. If you're willing to use rigid tubing, I think there are options like metal tubing with even lower permeability (but just because it's rigid doesn't mean it has lower permeability).
I ended up buying my tubing from Harrington Plastics, which has branches in the US. I think it was about $19 for the roll (I forget if it was 50' or 100').