🌿 CO2 pH KH Calculator
Estimate planted tank CO2 from pH and KH, then compare it with your degassed pH drop and livestock safety range.
| CO2 ppm | Typical Use | pH Drop Clue | Livestock Note |
|---|---|---|---|
| 3-10 | No injection / low tech | 0.0-0.5 | Gentle baseline |
| 10-20 | Easy plants, light CO2 | 0.5-0.8 | Usually safe for most fish |
| 20-30 | Common high-tech target | 0.8-1.0 | Watch behavior and oxygen |
| 30-40 | Demanding carpets / dense stems | 1.0-1.2 | Caution with shrimp and fry |
| 40+ | Special cases only | 1.2+ | High livestock stress risk |
| dKH | ppm as CaCO3 | Carbonate Buffer | CO2 Note |
|---|---|---|---|
| 1 | 17.8 ppm | Very low | pH moves quickly |
| 2 | 35.7 ppm | Low | Common soft planted range |
| 4 | 71.4 ppm | Moderate | Stable and easy to tune |
| 6 | 107.1 ppm | Firm | More CO2 needed for same pH |
| 8 | 142.8 ppm | High | Large pH changes need caution |
| 10 | 178.5 ppm | Very high | Verify target with livestock |
| Tank Style | Target CO2 | Typical pH Drop | KH Range |
|---|---|---|---|
| Low-tech planted | 5-10 ppm | 0.2-0.5 | 1-8 dKH |
| Shrimp planted | 10-20 ppm | 0.4-0.8 | 1-4 dKH |
| Community aquascape | 20-25 ppm | 0.8-0.95 | 2-6 dKH |
| High-tech stem tank | 25-35 ppm | 0.9-1.1 | 2-7 dKH |
| Advanced carpet tank | 30-40 ppm | 1.0-1.2 | 1-6 dKH |
When attempting to establish or maintain a planted aquarium, the plant may exhibit some growth within the aquarium, but not as much as is required for those planted species to thrive. The condition of the aquarium may reveal that there are some issues with the stems of the plant (indicating that the plants are not receiving enough carbon dioxide to facilitate growth) or that the plants may be patchily despite the addition of a significant amount of light to the aquarium. In these instances, it may be helpful to test the aquarium to determine if there is a need to add more or less carbon dioxide to the aquarium to facilitate the growth of those plants.
The relationship between pH, carbonate hardness, and carbon dioxide is one of the factors to consider within the aquarium. When carbon dioxide are added to the water in an aquarium, the carbon dioxide creates carbonic acid, which subsequently lowers the pH of the water. The degree to which the pH of the water drops is dependent upon the amount of carbonate hardness of the water.
How to Measure CO2 and Keep Plants and Fish Safe
Water that contains very low levels of carbonate hardness will experience a significant drop in pH when carbon dioxide is added to that water. In contrast, water with high carbonate hardness will absorb more carbon dioxide prior to the pH of the water change. A calculator that determines the relationship between these factors allow the user to input the pH and carbonate hardness levels of the aquarium to calculate the pH changes that will occur in the addition of carbon dioxide to the water.
One of the most important measurement of the water is the difference in pH between a sample of the water that does not contain carbon dioxide and the water that contains carbon dioxide being injected into the aquarium. The drop in pH is a measure of the amount of carbon dioxide that has been forced into the water. A tool that calculates the relationship between these factor allows for both pH readings to be entered into the tool, allowing it to calculate the difference between the two value.
In addition to measuring the drop in pH of the water, it is also helpful to calculate the amount of carbon dioxide necessary to provide enough to the planted aquarium’s livestock. While many may believe that adding more carbon dioxide will allow the plants to grow at a faster rate, the benefits of adding carbon dioxide to the water will plateau once the carbon dioxide is no longer a limiting factor for the plants in the planted aquarium. Beyond a certain saturation of carbon dioxide in the water, adding more carbon dioxide to the planted aquarium will result in the livestock of that planted aquarium experiencing detrimentally effects.
More sensitive species, such as shrimp and fry, will experience these detrimental effects more readily than more common community fish species due to the higher ratio of the surface area to the volume of these species. When carbon dioxide is added to the water, shrimp and fry will exhibit signs of stress more readily than community fish. The livestock safety selector allows for the user to choose the type of livestock that are to be added to or live within the planted aquarium.
Another factor in the calculation of the amount of carbon dioxide to be added to the planted aquarium is the difference between dKH and ppm as CaCO3. Different test kits will reveal different measurements of the carbonate hardness of the water; some will measure in degrees while others will measure in milligrams per liter. However, the two measurements are correlated with a fixed factor.
The carbonate hardness of the water can be used to calculate the amount of carbonic acid in the water; the carbonic acid can then reveal the amount of carbon dioxide that is currently contain within the planted aquarium. An additional factor to consider within the planted aquarium is the potential interference with the measurement of carbon dioxide. The substrate within the planted aquarium and any botanicals that are added to the aquarium can release organic acid into the water.
These organic acids will act as a buffer to the carbon dioxide in the water that is not related to the carbonate hardness calculations. These organic acids can lead to inaccuracies in the measurements of the amount of carbon dioxide within the planted aquarium. The buffer adjustment allows for the user to account for this interference of the substrate; without adjusting for this interference, the calculations may indicate that there are thirty parts per million of carbon dioxide in the planted aquarium when there are only twenty part per million of carbon dioxide in the planted aquarium.
Another factor that relates to the addition of carbon dioxide to the planted aquarium is the timing of when the water sample are taken. The pH of the planted aquarium should be measured after the carbon dioxide has had time to reach equilibrium within the water. The degassed water sample should also be allowed to release the carbon dioxide gas from the water sample; the water sample can be allowed to sit overnight to allow the carbon dioxide to leave the water.
If these measurements are too soon after the beginning of the addition of carbon dioxide into the planted aquarium, the calculated drop in pH may not be accurate. While the tool may be accurate in its calculations, it cannot compensate for taking measurements too quick of the planted aquarium. Aquariums contain factors that alter the equilibrium of the water; carbon dioxide is an example of such a gas.
The addition of carbon dioxide to the water will shift the equilibrium within the planted aquarium. In addition to the shift in the equilibrium of the water, the behaviors of the fish within the planted aquarium will shift; they will begin to exhibit rapid breathing. Additionally, shrimp will begin to exhibit clustering near the outflow of the planted aquarium.
These behaviors indicate that the amount of carbon dioxide injected into the planted aquarium should be decreased. Aeration should be increased. The behavior of the fish and shrimp should be continuous observed; the numbers are a helpful guide to the amount of carbon dioxide to add to the planted aquarium, but they are not a replacement for observing the behavior of the livestock of the planted aquarium.
Changing the carbonate hardness of the water will impact the amount of carbon dioxide that should be injected into the planted aquarium. For instance, raising the carbonate hardness of the planted aquarium will lead to increased stability of the water in the aquarium (there will be less shifts in pH), but more carbon dioxide will need to be injected into that planted aquarium to create the same degree of carbon dioxide saturation in the water. Lowering the carbonate hardness will make the carbon dioxide more responsive in the planted aquarium; lowering the carbonate hardness of the planted aquarium will allow for more rapidly shifts in pH.
However, there will be less room for error in the amount of carbon dioxide injected into the planted aquarium. The tools calculates the target pH for the amount of carbon dioxide that is to be injected into the planted aquarium. Thus, the user can understand if increasing or decreasing the carbonate hardness will be safe for the aquarium’s livestock.
The goal is to reach a stable point within the planted aquarium wherein the plants are receiving the amount of carbon dioxide necessary for growth, but the livestock are not stressed as a result of the saturation of carbon dioxide within the planted aquarium.
