Aquarium CO2 Bubble Rate Calculator
Get a safe starting CO2 injection rate in bubbles per second and per minute for a planted aquarium, based on tank volume and how heavily planted it is.
How it works
Bubbles/sec ≈ tank gallons × rate factor (0.05 low, 0.0667 medium, 0.1 high) · bubbles/min = bubbles/sec × 60
CO2 is the limiting nutrient in most planted tanks, but too much suffocates fish, so you dial it in gradually rather than setting a final number on day one. Bubble count from a diffuser is only a rough proxy — bubble size, diffuser efficiency and surface agitation all change how much gas actually dissolves — so treat this as a starting point and let a drop checker be the real judge. A green drop checker indicates roughly 30 ppm dissolved CO2, the sweet spot; blue means too little and yellow is a warning to cut back immediately.
Worked example
A 20-gallon moderately planted tank at the medium factor of 0.0667 starts at 20 × 0.0667 ≈ 1.33 bubbles per second, or about 80 bubbles per minute — roughly one bubble every 0.75 seconds.
Frequently asked questions
How fast should I raise the CO2?
Increase by only a small amount every few days and give the drop checker an hour or two to catch up, since it lags real CO2 levels. Rushing is the most common way hobbyists gas their fish.
Why is bubble count only a rough guide?
The same bubbles-per-second delivers different dissolved CO2 depending on bubble size, how efficient your diffuser is, and how much your filter and surface movement drive gas back out. Two identical bubble rates on different tanks can give very different ppm, which is why the drop checker is the real target.
Should CO2 run at night?
No. Plants only consume CO2 in light, so injecting at night just builds up gas and stresses fish. Put the CO2 on a timer or solenoid to start about an hour before the lights and stop an hour before they go off.
Related calculators
This calculator is for educational purposes. Double-check important results before acting on them.