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RE: CO2 cylinder question

I would avoid anything with a "medical" label because my HMO won't cover my
aquarium.  I do know that the cylinder lettering system has to do with
"metric" tanks.  US gas suppliers have a whole range of tank designations
that you can research on the web.

I have heard from several gas suppliers that there is really only one grade
of CO2 produced in the US, that is, a high purity "medical" grade.  Welding
(~99.5% CO2), beverage (~99.8%), and medical CO2 (~99.99%) all come from the
same source, the differences being introduced by the types of cylinders,
level of control, distributors procedures, etc.  One bad thing is water in
steel cylinders which interacts with the CO2 to form carbonic acid and rust
the cylinder.  Another bad thing is sulfur in beverage CO2 which can effect
the taste of your beer.  The third concern I've heard is dust and oil that
may clog metering valves/regulators.  I'm not sure what poisson could be in
99.8% CO2 that we should be worried about.  Has anyone ever gotten bad CO2
which killed fish or plants?  How about a clogged regulator?

Myself, I bought a new 10# aluminum cylinder from M3.  Since I had a new,
clean cylinder, I found a fire extinguisher company that would refill while
I waited.  They claim their CO2 is good for beverages as well.  I never let
it run to zero pressure, so no room air/water ever gets in.

Joe K