CO₂ Calculator
Aquarium CO₂ Calculator
Find your dissolved CO₂ level from pH and KH. See if it's safe for fish and optimal for plant growth.
Enter Your Water Parameters
12.0 ppm
Low, plants struggling
Formula: CO₂ = 3 × KH × 10(7.0 − pH)
Fish safety: CO₂ above 35 ppm can suffocate fish. Always use a drop checker and ensure good surface agitation. Turn CO₂ off at night or use a timer with your lighting period.
Why CO₂ Matters
Plants need carbon for photosynthesis. In most aquariums, dissolved CO₂ is the limiting nutrient. Supplementing CO₂ to 20–30 ppm dramatically improves plant growth, coloration, and the ability to out-compete algae. The pH/KH relationship lets you estimate CO₂ without an expensive meter.
pH / KH / CO₂ Reference (ppm)
| KH \ pH | 6.0 | 6.2 | 6.4 | 6.6 | 6.8 | 7.0 | 7.2 |
|---|---|---|---|---|---|---|---|
| 1 | 29.7 | 18.7 | 11.8 | 7.5 | 4.7 | 3 | 1.9 |
| 2 | 59.4 | 37.5 | 23.7 | 14.9 | 9.4 | 5.9 | 3.7 |
| 3 | 89.1 | 56.2 | 35.5 | 22.4 | 14.1 | 8.9 | 5.6 |
| 4 | 118.8 | 74.9 | 47.3 | 29.9 | 18.8 | 11.9 | 7.5 |
| 5 | 148.5 | 93.7 | 59.1 | 37.3 | 23.6 | 14.9 | 9.4 |
| 8 | 237.6 | 149.9 | 94.6 | 59.7 | 37.7 | 23.8 | 15 |
| 10 | 297 | 187.3 | 118.2 | 74.6 | 47.1 | 29.7 | 18.7 |
Green = optimal (15–35 ppm) · Yellow = low · Red = dangerous
Log your pH and KH over time with MyAquaLog to track CO₂ trends automatically.
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