CO² KH/PH Chart
This chart shows the dissolved carbon dioxide value of water based on the measurements of carbonate hardness (KH) and pH, which can be easily measured with a test kit. Bear in mind that these values can fluctuate throughout a 24hour period so any reading is only a guide.
For plant growth the ideal range of CO² is between 10-30ppm, and ideally 20-30ppm. This range is highlighted in green.
| pH | 6.0 | 6.2 | 6.4 | 6.6 | 6.8 | 7.0 | 7.2 | 7.4 | 7.6 | 7.8 | 8.0 | |
| KH | ||||||||||||
| 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 |
Note: ppm is the same as mg/l
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