Balance dissolved gas, hardness, and acidity with confidence. Get clear chemistry insights, exports, charts, and aquarium planning support.
The graph shows estimated pH across a practical CO2 range using your current KH value.
This calculator uses the common planted-aquarium approximation:
CO2 (ppm) = 3 × KH × 10(7 − pH)
Rearranged forms:
This relationship assumes carbonate hardness dominates buffering and that dissolved acids other than carbonic acid remain limited. It is useful for aquarium planning, but direct test-kit validation is still recommended.
| KH (dKH) | CO2 (ppm) | Estimated pH | Tank Volume (L) | CO2 Mass (g) |
|---|---|---|---|---|
| 3.0 | 15 | 6.778 | 60 | 0.900 |
| 4.0 | 20 | 6.778 | 100 | 2.000 |
| 5.0 | 30 | 6.699 | 150 | 4.500 |
| 6.0 | 35 | 6.711 | 200 | 7.000 |
It estimates the relationship between dissolved CO2, carbonate hardness, and pH. Aquarists often use it to plan gas injection and monitor whether tank acidity stays within a practical range.
No. It is an approximation that works best when carbonate hardness is the main buffer. Extra acids, bases, tannins, phosphate buffers, or unusual water chemistry can shift real measurements.
When CO2 dissolves, some forms carbonic acid. That increases hydrogen ion concentration and lowers pH. The effect depends on how strongly the water resists change through buffering.
Many planted aquariums target roughly 20 to 35 ppm during the photoperiod. Sensitive livestock may need less, so actual safe ranges should be confirmed gradually with observation and testing.
Tank volume helps estimate the total dissolved CO2 mass in the system. That gives extra context when comparing small and large aquariums with the same concentration value.
The core formula here does not directly adjust equilibrium constants with temperature. Still, temperature influences gas solubility and livestock stress, so it remains useful context during interpretation.
Use both together. Calculations are excellent for planning and trend checks, while calibrated pH tests, KH tests, and livestock behavior provide reality checks before major adjustments.
Only with caution. Complex systems often include extra buffering, aeration, and competing chemical species. For professional applications, use full carbonate equilibrium models and direct measurements.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.