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ARTICLE INFORMATION:

Author: Giancarlo Podio 
Title: CO2: KH/PH Chart
Summary: A chart that helps one determine how much CO2 they have in an aquarium by analyzing KH and PH levels.
Contact for editing purposes: theo@aquarticles.com
e-mail: tuvy72@hotmail.com
Date first published: March 2005
Publication: http://www.gpodio.com
Reprinted from Aquarticles:

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CO2: KH/PH Chart

By Giancarlo Podio
Aquarticles.com

PH is a result of carbonate hardness (KH) and CO2 concentration, meaning that we can calculate the amount of CO2 in a body of water by measuring KH and PH. For most of our tanks KH is stable while PH varies according to CO2 levels. As CO2 levels increase the PH goes down. By cross referencing your KH and PH values in the table below you can quickly find out the CO2 concentration in your tank.

pH 6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0
KHº
0.5 15 9.3 5.9 3.7 2.4 1.5 0.9 0.6 0.4 0.2 0.1
1.0 30 18.6 11.8 7.4 4.7 3 1.9 1.2 0.7 0.47 0.3
1.5 44 28 17.6 11.1 7 4.4 2.8 1.8 1.1 0.7 0.4
2.0 59 37 24 14.8 9.4 5.9 3.7 2.4 1.5 0.9 0.6
2.5 73 46 30 18.5 11.8 7.3 4.6 3 1.9 1.2 0.7
3.0 87 56 35 22 14 8.7 5.6 3.5 2.2 1.4 0.9
3.5 103 65 41 26 16.4 10.3 6.5 4.1 2.6 1.6 1
4.0 118 75 47 30 18.7 11.8 7.5 4.7 3 1.9 1.2
5.0 147 93 59 37 23 14.7 9.3 5.9 3.7 2.3 1.5
6.0 177 112 71 45 28 17.7 11.2 7.1 4.5 2.8 1.8
8.0 240 149 94 59 37 24 14.9 9.4 5.9 3.7 2.3
10 300 186 118 74 47 30 18.6 11.8 7.4 4.7 3
15 440 280 176 111 70 44 28 17.6 11.1 7 4.4
20 590 370 240 148 94 59 37 24 14.8 9.4 5.9

 

The ideal CO2 concentration for a CO2 enriched tank is anywhere between 15ppm and 30ppm (ppm = mg/lt). To simplify things the ideal range is highlighted in green. Red values indicate a CO2 level that is too high and potentially dangerous.