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[APD] RE: PPM Co2 gas in 5lb Cylinder

	>>Does anyone know the approximate PPM of Co2 gas in 5-lb of Co2?<<

I think you probably asked the wrong question. PPM is shorthand for Parts
Per Million, and is used to indicate the concentration of one substance in
another. One ppm is equal to 0.0001%, ten ppm is 0.001%, one hundred ppm is
0.01%, one thousand ppm is 0.1%, ten thousand ppm is 1.0%, one hundred
thousand ppm is 10% and one million ppm is 100%.

For instance, if you have a mixture that is 75 percent of X substance and 25
percent Y substance, it would be 750,000 ppm of X and 250,000 ppm of Y. To
put it in numbers more suitable to the topic, if there is 15 ppm CO2 in your
aquarium water, that means that there is 0.0015 percent CO2, the rest being
something else, like water, salt, oxygen, and other dissolved substances.

To answer your question the purity of CO2 in most cylinders used on our
tanks probably runs 98% or better which is 980,000 ppm, with the rest
probably being nitrogen, oxygen few other gases, and even trace amounts of
water. I don't really think that is the information you were looking for,
but there it is. Higher purity grades are available, at a price. Some are
processed for very low oxygen, some for very low moisture. Some are
processed for very high overall purity with the impurities measured in the
parts per billion range.

	>>What would be the volume of Co2 gas from a 5-lb cylinder were it
released to the atmosphere?<<

According to information from the Carbon Dioxide Division of AmeriGas, one
pound of liquid CO2 would have a volume of  8.59 cubic feet (243.2 liters)
if allowed to vaporize. Therefore 5 pounds of CO2 will yield 42.95 cubic
feet (1216.2 liters) of gas.

How does all of this translate into "How many pounds of CO2 do I need to
maintain the water in my fish tank at 15 ppm CO2?" That is a question we
don't have enough information to answer. It depends on how much water is in
your tank, how many and what kinds of plants you have, how much plant food
is in the water (which determines how fast the plants use the CO2), how
effectively you dissolve the CO2 in the water, how fast the CO2 escapes into
the air (which is dependant on water temperature, agitation, and other
factors), how many fish you have making more CO2 (a very small influence, I
would think), and a host of other factors. Possibly even the buffering
capacity of the water (Do higher carbonate concentrations "bind" the CO2 and
help keep it from evolving from the water?).

Hope that helped. If not, sorry for wasting your time.

Douglas Guynn
	d.guynn at sbcglobal.net

Not everyone who says to Me, 'Lord, Lord,' will enter the kingdom of heaven;
but he who does the will of My Father who is in heaven. Matt 7:21

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