I found this article on the webby,
Subject: CO2 purity?
> CO2 is not very pure? Is there differen't grades of C02?
> The idea of not getting pure co2 is troubling to me, since I too
> had similar problems as the original poster with not being able
> my pH.
There are at least two different grades of CO2 available, (I found
out during a similar problem) Food grade, which is used in soda
machines and such, and commercial grade, which is used in some
welding applications from what I can tell. The food grade is what
The only difference between these two grades of CO2 is that the
bottle that it comes in. Both gases are 99.97% CO2, the food
grade bottles are internally glass coated, whereas the industrial
cylinders are straight steel.
The reason that there is a difference, is that by law, the food
systems have the possibility of back-flowing into the bottle
when the gas runs out. If the bottle was a standard industrial
bottle, the system would have the possibility of becoming
contaminated with rust from the internals of the bottle. (CO2
disolved in liquid from beverages is quite acidic and rusts the
inside of gas cylinders.
This would be the same as eating tinned food where the can
was rusting, you have the risk of contracting tetnis(?)(lock-jaw)
or some other illness associated with rust.
So the insides of food grade cylinders are washed each time
before the bottle gets refilled according to food hygene laws.
Therefore the food grade bottles are more expensive to hire, as
more work goes into refilling. According to the rules you are not
really permitted to use food grade CO2 for fish tanks, as what
you are hooking up to them is not passed by the food hygene
act, but I know that people do.
The only thing is that industrial CO2 is cheaper because there
is less involved in refilling cylinders, and has the same purity,
so that is why I use it.
Originally Posted by oldschool
you'll do anything for *****.....