pH drop CO2 chart

Tom Barr

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Jan 23, 2005
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Table: CO2 concentrations (ppm) in relation to estimated (equilibrium) concentration in degassed water and pH drop.
Estimated CO2 concentration (ppm) in degassed water
0.5 1.0 1.5 2.0 2.5 3.0
pH drop
0.0 0.5 1 1.5 2.0 2.5 3.0
0.1 0.6 1.3 1.9 2.5 3.1 3.8
0.2 0.8 1.6 2.4 3.2 4.0 4.8
0.3 1.0 2.0 3.0 4.0 5.0 6.0
0.4 1.3 2.5 3.8 5.0 6.3 7.5
0.5 1.6 3.2 4.7 6.3 7.9 9.5
0.6 2.0 4.0 6.0 8.0 10.0 11.9
0.7 2.5 5.0 7.5 10.0 12.5 15.0
0.8 3.2 6.3 9.5 12.6 15.8 18.9
0.9 4.0 7.9 11.9 15.9 19.9 23.8
1 5.0 10.0 15.0 20.0 25.0 30.0
1.1 6.3 12.6 18.9 25.2 31.5 37.8
1.2 7.9 15.8 23.8 31.7 39.6 47.5
1.3 10.0 20.0 29.9 39.9 49.9 59.9
1.4 12.6 25.1 37.7 50.2 62.8 75.4
1.5 15.8 31.6 47.4 63.2 79.1 94.9
1.6 19.9 39.8 59.7 79.6 99.5 119.4
1.7 25.1 50.1 75.2 100.2 125.3 150.4
1.8 31.5 63.1 94.6 126.2 157.7 189.3
1.9 39.7 79.4 119.1 158.9 198.6 238.3
2 50.0 100.0 150.0 200.0 250.0 300.0

Notes:

There are definitely some serious limitations to using the pH drop method to determine CO2 concentrations. Most important is that while there is going to be a theoretical concentration of CO2 in water at equilibrium with the atmosphere, in reality achieving this equilibrium is probably very hard. Factors such as higher CO2 concentrations found in buildings, the long time period needed to achieve equilibrium, organic material in the water, and the potential for evaporation to increase KH may all cause variation in the level reached. The real issue is that a difference of say 1ppm in the assumption made about the CO2 concentration of the degassed water will relate to a very large difference in the assumed CO2 level in the aquarium once the pH has been dropped by 1 unit or more. This essentially makes this method inaccurate and points the drop checker method as been preferable.

Cheers

Neil
 

MTechnik

Junior Poster
Apr 13, 2007
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[FONT="Courier New"]Table: CO2 concentrations (ppm) in relation to estimated (equilibrium) concentration in degassed water and pH drop.
Estimated CO2 concentration (ppm) in degassed water
0.5 1.0 1.5 2.0 2.5 3.0
pH drop
0.0  0.5  1     1.5   2.0   2.5   3.0
0.1  0.6  1.3   1.9   2.5   3.1   3.8
0.2  0.8  1.6   2.4   3.2   4.0   4.8
0.3  1.0  2.0   3.0   4.0   5.0   6.0
0.4  1.3  2.5   3.8   5.0   6.3   7.5
0.5  1.6  3.2   4.7   6.3   7.9   9.5
0.6  2.0  4.0   6.0   8.0   10.0  11.9
0.7  2.5  5.0   7.5   10.0  12.5  15.0
0.8  3.2  6.3   9.5   12.6  15.8  18.9
0.9  4.0  7.9   11.9  15.9  19.9  23.8
1    5.0  10.0  15.0  20.0  25.0  30.0
1.1  6.3  12.6  18.9  25.2  31.5  37.8
1.2  7.9  15.8  23.8  31.7  39.6  47.5
1.3  10.0 20.0  29.9  39.9  49.9  59.9
1.4  12.6 25.1  37.7  50.2  62.8  75.4
1.5  15.8 31.6  47.4  63.2  79.1  94.9
1.6  19.9 39.8  59.7  79.6  99.5  119.4
1.7  25.1 50.1  75.2  100.2 125.3 150.4
1.8  31.5 63.1  94.6  126.2 157.7 189.3
1.9  39.7 79.4  119.1 158.9 198.6 238.3
2    50.0 100.0 150.0 200.0 250.0 300.0
[/FONT]

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