Planted tank calculator
CO2 PPM pH KH Calculator
Estimate dissolved CO2 from pH and carbonate hardness for a freshwater planted aquarium.
How this calculator works
The calculator uses the common planted-tank estimate: CO2 ppm is approximately 3 times KH times 10 to the power of 7 minus pH. KH is entered as degrees of carbonate hardness.
Why it matters
CO2 can improve plant growth, but unstable or excessive CO2 stresses fish and shrimp. The estimate gives a planning number while the real safety check remains livestock behavior, surface movement, and gradual adjustment.
Worked example
At pH 6.8 and KH 4 dKH, the estimate is 3 x 4 x 10^(7 - 6.8), or about 19 ppm CO2. That falls inside the common planted target range.
FAQ
What target CO2 range is common for planted tanks?
Many planted aquariums aim around 15-30 ppm, but livestock behavior matters more than a number.
Why can this estimate be wrong?
The formula assumes carbonate buffering. Phosphates, tannins, acids, and other buffers can change pH without matching CO2.
Should I chase pH with CO2?
No. Use CO2 slowly, watch livestock, and treat pH drop as one signal rather than the goal itself.
Does this work for saltwater?
No. It is intended for freshwater planted aquariums using KH and pH as a rough CO2 estimate.