# [APD] Re: CO2 off at night

```Robert Paul Hudson wonders:

> I thought 30 mg/L [of CO2] equaled somewhere between
> 20 and 30ppm. Is it lower than that?

[Gee, I hope I remember how to use the metric system or I'm going to be
thoroughly embarrased and will have to go back to Lurk Mode]

Let's see.  Considering pure water:

One liter of water is 1000 cubic centimeters. A gram is [was?] defined as one
cubic centimeter of water. Therefore one liter of water is 1000 grams.

One milligram of water is 0.001 grams.

Thus a "mg/l" is 0.001 grams (or parts) per 1000 grams (or parts). Multiplying
by 1000 gives us:

1 part per 1,000,000 parts

or approximately "one part per million".

But of course we aren't talking about pure water. We are talking about
milligrams of CO2 per liter of solution. But unless you are anal-rententive, we
are still talking 1 mg/l is approximately 1 part per million.

Paul probably already knew this but the derivation is fun anyway.

George Booth in Ft. Collins, CO (gbooth at frii dot com)
The website for Aquatic Gardeners by Aquatic Gardeners
http://aquaticconcepts.thekrib.com/  (mirror)
http://www.frii.com/~gbooth/AquaticConcepts/

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