CO2 Calculator
Estimate CO2 levels from pH and KH, and target bubble rates.
How it works
Dissolved CO2 (ppm) ≈ 3 × KH × 10^(7 − pH). Aim for 20-30 ppm for planted tanks. Bubble rate is tank-specific; start around 1 bubble/second per 100 L and tune using a drop checker (green = good).
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Formula & Method
Dissolved CO2 (ppm) ≈ 3 × KH × 10^(7 − pH). Aim for 20-30 ppm for planted tanks. Bubble rate is tank-specific; start around 1 bubble/second per 100 L and tune using a drop checker (green = good).
Example Calculation
At pH 6.8 and KH 4: CO2 ≈ 3 × 4 × 10^(7−6.8) = 12 × 10^0.2 ≈ 19 ppm — slightly low, so increase injection toward 25 ppm.
Frequently Asked Questions
How much CO2 does a planted tank need?
Around 30 ppm dissolved CO2 during the photoperiod suits most high-tech planted tanks. Below 15 ppm, demanding plants will not thrive; above 35-40 ppm you risk the fish.
What colour should my drop checker be?
Green, using 4 dKH reference solution rather than tank water. Blue means too little CO2, yellow means too much. The reading lags the tank by one to two hours.
When should CO2 turn on and off?
Start one to two hours before the lights and stop about an hour before they go off. Plants cannot use CO2 in darkness, and overnight accumulation lowers pH and stresses fish.
Can I run a planted tank without CO2?
Yes. Anubias, java fern, cryptocorynes, vallisneria, bucephalandra and most mosses grow well without injection. Carpeting plants and most stem plants with red colouration will disappoint you without it.
Is liquid carbon a substitute for CO2 injection?
Not really. Glutaraldehyde-based products have some algaecidal effect and a modest carbon benefit, but they do not replace injected CO2 for demanding plants.