Aquarium CO₂ Calculator
THE WET LEAF · AQUASCAPING ACADEMY
Two measurements. One useful estimate. Explore the relationship between pH, carbonate hardness and dissolved CO₂ in your planted aquarium.
Your water measurements
Enter your measured pH and KH. Results update as you type.
Use dKH, not GH or ppm hardness. Supported inputs: pH 0–14 and KH above 0 up to 50 dKH. Very low KH makes the estimate especially uncertain.
A guide, not a guarantee
Around 20–30 ppm is a general reference for many CO₂-injected planted tanks, not a universally safe target. Low-tech aquariums do not need to reach it. Livestock tolerance, oxygen levels and gas exchange matter. If fish gasp or show distress, stop CO₂ injection and increase aeration immediately.
Explore the pH / KH reference chart
Find your dKH row and pH column. All values are estimated CO₂ in ppm, calculated with the same formula. Swipe or scroll sideways on smaller screens.
Colours follow the uploaded reference chart. The green band is broader than the 20–30 ppm general guidance; no colour guarantees livestock safety. Colours use unrounded values.
| dKH / pH | 6.0 | 6.1 | 6.2 | 6.3 | 6.4 | 6.5 | 6.6 | 6.7 | 6.8 | 6.9 | 7.0 | 7.1 | 7.2 | 7.3 | 7.4 | 7.5 | 7.6 | 7.7 | 7.8 | 7.9 | 8.0 | 8.1 | 8.2 | 8.3 | 8.4 | 8.5 | 8.6 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0.5 | 15.0 | 11.9 | 9.5 | 7.5 | 6.0 | 4.7 | 3.8 | 3.0 | 2.4 | 1.9 | 1.5 | 1.2 | 0.9 | 0.8 | 0.6 | 0.5 | 0.4 | 0.3 | 0.2 | 0.2 | 0.2 | 0.1 | 0.1 | 0.1 | 0.1 | <0.1 | <0.1 |
| 1 | 30.0 | 23.8 | 18.9 | 15.0 | 11.9 | 9.5 | 7.5 | 6.0 | 4.8 | 3.8 | 3.0 | 2.4 | 1.9 | 1.5 | 1.2 | 0.9 | 0.8 | 0.6 | 0.5 | 0.4 | 0.3 | 0.2 | 0.2 | 0.2 | 0.1 | 0.1 | 0.1 |
| 1.5 | 45.0 | 35.7 | 28.4 | 22.6 | 17.9 | 14.2 | 11.3 | 9.0 | 7.1 | 5.7 | 4.5 | 3.6 | 2.8 | 2.3 | 1.8 | 1.4 | 1.1 | 0.9 | 0.7 | 0.6 | 0.5 | 0.4 | 0.3 | 0.2 | 0.2 | 0.1 | 0.1 |
| 2 | 60.0 | 47.7 | 37.9 | 30.1 | 23.9 | 19.0 | 15.1 | 12.0 | 9.5 | 7.6 | 6.0 | 4.8 | 3.8 | 3.0 | 2.4 | 1.9 | 1.5 | 1.2 | 1.0 | 0.8 | 0.6 | 0.5 | 0.4 | 0.3 | 0.2 | 0.2 | 0.2 |
| 2.5 | 75.0 | 59.6 | 47.3 | 37.6 | 29.9 | 23.7 | 18.8 | 15.0 | 11.9 | 9.4 | 7.5 | 6.0 | 4.7 | 3.8 | 3.0 | 2.4 | 1.9 | 1.5 | 1.2 | 0.9 | 0.8 | 0.6 | 0.5 | 0.4 | 0.3 | 0.2 | 0.2 |
| 3 | 90.0 | 71.5 | 56.8 | 45.1 | 35.8 | 28.5 | 22.6 | 18.0 | 14.3 | 11.3 | 9.0 | 7.1 | 5.7 | 4.5 | 3.6 | 2.8 | 2.3 | 1.8 | 1.4 | 1.1 | 0.9 | 0.7 | 0.6 | 0.5 | 0.4 | 0.3 | 0.2 |
| 3.5 | 105.0 | 83.4 | 66.3 | 52.6 | 41.8 | 33.2 | 26.4 | 21.0 | 16.6 | 13.2 | 10.5 | 8.3 | 6.6 | 5.3 | 4.2 | 3.3 | 2.6 | 2.1 | 1.7 | 1.3 | 1.1 | 0.8 | 0.7 | 0.5 | 0.4 | 0.3 | 0.3 |
| 4 | 120.0 | 95.3 | 75.7 | 60.1 | 47.8 | 37.9 | 30.1 | 23.9 | 19.0 | 15.1 | 12.0 | 9.5 | 7.6 | 6.0 | 4.8 | 3.8 | 3.0 | 2.4 | 1.9 | 1.5 | 1.2 | 1.0 | 0.8 | 0.6 | 0.5 | 0.4 | 0.3 |
| 4.5 | 135.0 | 107.2 | 85.2 | 67.7 | 53.7 | 42.7 | 33.9 | 26.9 | 21.4 | 17.0 | 13.5 | 10.7 | 8.5 | 6.8 | 5.4 | 4.3 | 3.4 | 2.7 | 2.1 | 1.7 | 1.4 | 1.1 | 0.9 | 0.7 | 0.5 | 0.4 | 0.3 |
| 5 | 150.0 | 119.1 | 94.6 | 75.2 | 59.7 | 47.4 | 37.7 | 29.9 | 23.8 | 18.9 | 15.0 | 11.9 | 9.5 | 7.5 | 6.0 | 4.7 | 3.8 | 3.0 | 2.4 | 1.9 | 1.5 | 1.2 | 0.9 | 0.8 | 0.6 | 0.5 | 0.4 |
| 5.5 | 165.0 | 131.1 | 104.1 | 82.7 | 65.7 | 52.2 | 41.4 | 32.9 | 26.2 | 20.8 | 16.5 | 13.1 | 10.4 | 8.3 | 6.6 | 5.2 | 4.1 | 3.3 | 2.6 | 2.1 | 1.7 | 1.3 | 1.0 | 0.8 | 0.7 | 0.5 | 0.4 |
| 6 | 180.0 | 143.0 | 113.6 | 90.2 | 71.7 | 56.9 | 45.2 | 35.9 | 28.5 | 22.7 | 18.0 | 14.3 | 11.4 | 9.0 | 7.2 | 5.7 | 4.5 | 3.6 | 2.9 | 2.3 | 1.8 | 1.4 | 1.1 | 0.9 | 0.7 | 0.6 | 0.5 |
| 6.5 | 195.0 | 154.9 | 123.0 | 97.7 | 77.6 | 61.7 | 49.0 | 38.9 | 30.9 | 24.5 | 19.5 | 15.5 | 12.3 | 9.8 | 7.8 | 6.2 | 4.9 | 3.9 | 3.1 | 2.5 | 2.0 | 1.5 | 1.2 | 1.0 | 0.8 | 0.6 | 0.5 |
| 7 | 210.0 | 166.8 | 132.5 | 105.2 | 83.6 | 66.4 | 52.7 | 41.9 | 33.3 | 26.4 | 21.0 | 16.7 | 13.3 | 10.5 | 8.4 | 6.6 | 5.3 | 4.2 | 3.3 | 2.6 | 2.1 | 1.7 | 1.3 | 1.1 | 0.8 | 0.7 | 0.5 |
| 7.5 | 225.0 | 178.7 | 142.0 | 112.8 | 89.6 | 71.2 | 56.5 | 44.9 | 35.7 | 28.3 | 22.5 | 17.9 | 14.2 | 11.3 | 9.0 | 7.1 | 5.7 | 4.5 | 3.6 | 2.8 | 2.2 | 1.8 | 1.4 | 1.1 | 0.9 | 0.7 | 0.6 |
| 8 | 240.0 | 190.6 | 151.4 | 120.3 | 95.5 | 75.9 | 60.3 | 47.9 | 38.0 | 30.2 | 24.0 | 19.1 | 15.1 | 12.0 | 9.6 | 7.6 | 6.0 | 4.8 | 3.8 | 3.0 | 2.4 | 1.9 | 1.5 | 1.2 | 1.0 | 0.8 | 0.6 |
| 8.5 | 255.0 | 202.6 | 160.9 | 127.8 | 101.5 | 80.6 | 64.1 | 50.9 | 40.4 | 32.1 | 25.5 | 20.3 | 16.1 | 12.8 | 10.2 | 8.1 | 6.4 | 5.1 | 4.0 | 3.2 | 2.6 | 2.0 | 1.6 | 1.3 | 1.0 | 0.8 | 0.6 |
| 9 | 270.0 | 214.5 | 170.4 | 135.3 | 107.5 | 85.4 | 67.8 | 53.9 | 42.8 | 34.0 | 27.0 | 21.4 | 17.0 | 13.5 | 10.7 | 8.5 | 6.8 | 5.4 | 4.3 | 3.4 | 2.7 | 2.1 | 1.7 | 1.4 | 1.1 | 0.9 | 0.7 |
| 9.5 | 285.0 | 226.4 | 179.8 | 142.8 | 113.5 | 90.1 | 71.6 | 56.9 | 45.2 | 35.9 | 28.5 | 22.6 | 18.0 | 14.3 | 11.3 | 9.0 | 7.2 | 5.7 | 4.5 | 3.6 | 2.9 | 2.3 | 1.8 | 1.4 | 1.1 | 0.9 | 0.7 |
| 10 | 300.0 | 238.3 | 189.3 | 150.4 | 119.4 | 94.9 | 75.4 | 59.9 | 47.5 | 37.8 | 30.0 | 23.8 | 18.9 | 15.0 | 11.9 | 9.5 | 7.5 | 6.0 | 4.8 | 3.8 | 3.0 | 2.4 | 1.9 | 1.5 | 1.2 | 0.9 | 0.8 |
| 10.5 | 315.0 | 250.2 | 198.8 | 157.9 | 125.4 | 99.6 | 79.1 | 62.9 | 49.9 | 39.7 | 31.5 | 25.0 | 19.9 | 15.8 | 12.5 | 10.0 | 7.9 | 6.3 | 5.0 | 4.0 | 3.2 | 2.5 | 2.0 | 1.6 | 1.3 | 1.0 | 0.8 |
| 11 | 330.0 | 262.1 | 208.2 | 165.4 | 131.4 | 104.4 | 82.9 | 65.8 | 52.3 | 41.5 | 33.0 | 26.2 | 20.8 | 16.5 | 13.1 | 10.4 | 8.3 | 6.6 | 5.2 | 4.2 | 3.3 | 2.6 | 2.1 | 1.7 | 1.3 | 1.0 | 0.8 |
| 11.5 | 345.0 | 274.0 | 217.7 | 172.9 | 137.3 | 109.1 | 86.7 | 68.8 | 54.7 | 43.4 | 34.5 | 27.4 | 21.8 | 17.3 | 13.7 | 10.9 | 8.7 | 6.9 | 5.5 | 4.3 | 3.5 | 2.7 | 2.2 | 1.7 | 1.4 | 1.1 | 0.9 |
| 12 | 360.0 | 286.0 | 227.1 | 180.4 | 143.3 | 113.8 | 90.4 | 71.8 | 57.1 | 45.3 | 36.0 | 28.6 | 22.7 | 18.0 | 14.3 | 11.4 | 9.0 | 7.2 | 5.7 | 4.5 | 3.6 | 2.9 | 2.3 | 1.8 | 1.4 | 1.1 | 0.9 |
| 12.5 | 375.0 | 297.9 | 236.6 | 187.9 | 149.3 | 118.6 | 94.2 | 74.8 | 59.4 | 47.2 | 37.5 | 29.8 | 23.7 | 18.8 | 14.9 | 11.9 | 9.4 | 7.5 | 5.9 | 4.7 | 3.8 | 3.0 | 2.4 | 1.9 | 1.5 | 1.2 | 0.9 |
| 13 | 390.0 | 309.8 | 246.1 | 195.5 | 155.3 | 123.3 | 98.0 | 77.8 | 61.8 | 49.1 | 39.0 | 31.0 | 24.6 | 19.5 | 15.5 | 12.3 | 9.8 | 7.8 | 6.2 | 4.9 | 3.9 | 3.1 | 2.5 | 2.0 | 1.6 | 1.2 | 1.0 |
| 13.5 | 405.0 | 321.7 | 255.5 | 203.0 | 161.2 | 128.1 | 101.7 | 80.8 | 64.2 | 51.0 | 40.5 | 32.2 | 25.6 | 20.3 | 16.1 | 12.8 | 10.2 | 8.1 | 6.4 | 5.1 | 4.0 | 3.2 | 2.6 | 2.0 | 1.6 | 1.3 | 1.0 |
| 14 | 420.0 | 333.6 | 265.0 | 210.5 | 167.2 | 132.8 | 105.5 | 83.8 | 66.6 | 52.9 | 42.0 | 33.4 | 26.5 | 21.0 | 16.7 | 13.3 | 10.5 | 8.4 | 6.7 | 5.3 | 4.2 | 3.3 | 2.7 | 2.1 | 1.7 | 1.3 | 1.1 |
| 14.5 | 435.0 | 345.5 | 274.5 | 218.0 | 173.2 | 137.6 | 109.3 | 86.8 | 68.9 | 54.8 | 43.5 | 34.6 | 27.4 | 21.8 | 17.3 | 13.8 | 10.9 | 8.7 | 6.9 | 5.5 | 4.4 | 3.5 | 2.7 | 2.2 | 1.7 | 1.4 | 1.1 |
| 15 | 450.0 | 357.4 | 283.9 | 225.5 | 179.1 | 142.3 | 113.0 | 89.8 | 71.3 | 56.7 | 45.0 | 35.7 | 28.4 | 22.6 | 17.9 | 14.2 | 11.3 | 9.0 | 7.1 | 5.7 | 4.5 | 3.6 | 2.8 | 2.3 | 1.8 | 1.4 | 1.1 |
| 15.5 | 465.0 | 369.4 | 293.4 | 233.1 | 185.1 | 147.0 | 116.8 | 92.8 | 73.7 | 58.5 | 46.5 | 36.9 | 29.3 | 23.3 | 18.5 | 14.7 | 11.7 | 9.3 | 7.4 | 5.9 | 4.7 | 3.7 | 2.9 | 2.3 | 1.9 | 1.5 | 1.2 |
| 16 | 480.0 | 381.3 | 302.9 | 240.6 | 191.1 | 151.8 | 120.6 | 95.8 | 76.1 | 60.4 | 48.0 | 38.1 | 30.3 | 24.1 | 19.1 | 15.2 | 12.1 | 9.6 | 7.6 | 6.0 | 4.8 | 3.8 | 3.0 | 2.4 | 1.9 | 1.5 | 1.2 |
| 16.5 | 495.0 | 393.2 | 312.3 | 248.1 | 197.1 | 156.5 | 124.3 | 98.8 | 78.5 | 62.3 | 49.5 | 39.3 | 31.2 | 24.8 | 19.7 | 15.7 | 12.4 | 9.9 | 7.8 | 6.2 | 5.0 | 3.9 | 3.1 | 2.5 | 2.0 | 1.6 | 1.2 |
| 17 | 510.0 | 405.1 | 321.8 | 255.6 | 203.0 | 161.3 | 128.1 | 101.8 | 80.8 | 64.2 | 51.0 | 40.5 | 32.2 | 25.6 | 20.3 | 16.1 | 12.8 | 10.2 | 8.1 | 6.4 | 5.1 | 4.1 | 3.2 | 2.6 | 2.0 | 1.6 | 1.3 |
| 17.5 | 525.0 | 417.0 | 331.3 | 263.1 | 209.0 | 166.0 | 131.9 | 104.8 | 83.2 | 66.1 | 52.5 | 41.7 | 33.1 | 26.3 | 20.9 | 16.6 | 13.2 | 10.5 | 8.3 | 6.6 | 5.2 | 4.2 | 3.3 | 2.6 | 2.1 | 1.7 | 1.3 |
| 18 | 540.0 | 428.9 | 340.7 | 270.6 | 215.0 | 170.8 | 135.6 | 107.7 | 85.6 | 68.0 | 54.0 | 42.9 | 34.1 | 27.1 | 21.5 | 17.1 | 13.6 | 10.8 | 8.6 | 6.8 | 5.4 | 4.3 | 3.4 | 2.7 | 2.1 | 1.7 | 1.4 |
| 18.5 | 555.0 | 440.9 | 350.2 | 278.2 | 220.9 | 175.5 | 139.4 | 110.7 | 88.0 | 69.9 | 55.5 | 44.1 | 35.0 | 27.8 | 22.1 | 17.6 | 13.9 | 11.1 | 8.8 | 7.0 | 5.6 | 4.4 | 3.5 | 2.8 | 2.2 | 1.8 | 1.4 |
| 19 | 570.0 | 452.8 | 359.6 | 285.7 | 226.9 | 180.2 | 143.2 | 113.7 | 90.3 | 71.8 | 57.0 | 45.3 | 36.0 | 28.6 | 22.7 | 18.0 | 14.3 | 11.4 | 9.0 | 7.2 | 5.7 | 4.5 | 3.6 | 2.9 | 2.3 | 1.8 | 1.4 |
| 19.5 | 585.0 | 464.7 | 369.1 | 293.2 | 232.9 | 185.0 | 146.9 | 116.7 | 92.7 | 73.6 | 58.5 | 46.5 | 36.9 | 29.3 | 23.3 | 18.5 | 14.7 | 11.7 | 9.3 | 7.4 | 5.9 | 4.6 | 3.7 | 2.9 | 2.3 | 1.8 | 1.5 |
| 20 | 600.0 | 476.6 | 378.6 | 300.7 | 238.9 | 189.7 | 150.7 | 119.7 | 95.1 | 75.5 | 60.0 | 47.7 | 37.9 | 30.1 | 23.9 | 19.0 | 15.1 | 12.0 | 9.5 | 7.6 | 6.0 | 4.8 | 3.8 | 3.0 | 2.4 | 1.9 | 1.5 |
Understand your result
How is the estimate calculated?
CO₂ (ppm) = 3 × KH (dKH) × 10^(7 − pH). For example, pH 6.6 and KH 4 gives approximately 30.1 ppm. A change of 0.1 pH changes the estimate by about 26%, so use careful measurements and a calibrated pH meter or suitable test kit.
Why do active aquasoils and other buffers matter?
The equation treats carbonate chemistry as the main source of buffering. Active soils, humic acids, peat, phosphate buffers and pH-adjusting products can alter pH or the interpretation of a KH test independently of dissolved CO₂. The calculator cannot correct for those effects. A high result in such water does not prove high CO₂.
How should I read a drop checker?
With a proper 4 dKH reference solution and suitable indicator, blue generally suggests lower CO₂, green the intended range, and yellow potentially excessive CO₂. This colour guide does not apply to checkers filled with aquarium water. Follow the checker and solution manufacturer’s instructions. Drop checkers respond slowly, often over hours, and cannot warn immediately after an adjustment. Observe livestock directly.
Can this tell me my bubble rate?
No. Bubble size, counter design, diffuser efficiency, circulation and surface exchange vary. Bubbles per second cannot be converted reliably into ppm. Make small adjustments, allow the system to stabilise, and use consistent measurements together with livestock observation. Do not chase a pH number by adding acids.