CO2 // 04|PLANTED TANK DOSING
CO₂ Bubble Rate & Dosing Calculator.
Determine dissolved CO₂ ppm from pH & dKH, and calibrate safe bubble counter rates.
DISSOLVED CO₂ CONCENTRATION
21.3 ppm CO₂
Optimal for Planted Tank
TARGET CO₂ RANGE
20.0 - 30.0 ppm
Planted tank standard
START BUBBLE RATE
2.4 BPS
Bubbles per second
BUBBLES PER MINUTE
145 BPM
Bubble counter frequency
pH DROP TO TARGET
↓ 0.15 pH
To reach 30 ppm target
FAQ
Planted tank CO2 questions.
Where the pH and dKH formula comes from, what concentration to aim for, and the common measurement pitfalls that make CO2 readings misleading.
How is dissolved CO2 calculated from pH and dKH?
The standard hobbyist formula is CO2 in ppm equals 3.0 multiplied by dKH, multiplied by 10 to the power of (7 minus pH). It derives from the carbonate equilibrium that links pH, carbonate hardness, and dissolved carbon dioxide. The estimate assumes your carbonate hardness comes from carbonates and that no other acids or buffers are skewing pH.
What CO2 level should a planted tank target?
Between 20 and 30 ppm is the accepted sweet spot, with 30 ppm treated as the high-tech standard for demanding plants under strong light. Above roughly 35 ppm fish begin to show stress, so 30 ppm is a ceiling rather than a goal to exceed. Low-tech tanks grow perfectly well at lower levels with slower-growing species.
How many bubbles per second do I need?
For tanks up to about 200 litres, one to three bubbles per second is usually enough to reach a green drop checker. Bubble size varies between diffusers and regulators, so bubbles per second is only a starting reference, never an absolute dose. Begin conservatively, then adjust over several days while watching your drop checker and your fish.
Why is my pH-and-dKH CO2 reading inaccurate?
The calculation assumes carbonate alkalinity is the only buffer present. Phosphate buffers, tannins from driftwood, peat, some commercial pH adjusters, and non-carbonate hardness all distort the relationship and usually make CO2 appear higher than it is. Cross-check with a drop checker filled with 4 dKH reference solution, which responds only to dissolved CO2.
What does the pH drop method mean?
Because dissolved CO2 acidifies water predictably, the pH difference between fully degassed water and your running tank indicates CO2 concentration. A drop of about 1.0 pH unit from the degassed baseline corresponds to roughly 30 ppm. Measure the baseline by leaving a sample out overnight, or aerating it vigorously, before comparing.
Should I turn CO2 off at night?
Yes, for most systems. Plants only consume CO2 in the light, so injecting after dark drives levels up while plants and fish both consume oxygen, which is when suffocation risk peaks. A solenoid on a timer that starts one to two hours before lights on and stops shortly before lights off is standard practice, and it conserves gas.