Aquarium CO2 Injection Rate Calculator

Demanding planted aquariums live or die by their CO2 supply. The ideal dissolved CO2 concentration for most planted tanks is 20–30 ppm (parts per million). Below 15 ppm, many plants struggle. Above 35 ppm, fish and shrimp may show signs of distress.

Estimating CO2 Demand

The baseline CO2 injection rate depends on tank volume and how quickly CO2 is consumed or off-gassed. A common starting formula is:

CO2 Rate (bubbles per second) = Tank Volume (L) × Plant Factor × Light Factor / 60

Where:

• Plant Factor: Low density = 0.5, Medium = 1.0, High = 1.5, Very High (Dutch/Iwagumi) = 2.0
• Light Factor: Low light (< 30 PAR, photosynthetically active radiation) = 0.5, Medium (30–60 PAR) = 1.0, High (60–120 PAR) = 1.5, Very High (> 120 PAR) = 2.0

Worked Example

A 200-liter tank with high plant density and medium lighting: CO2 Rate = 200 × 1.5 × 1.0 / 60 = 5.0 bubbles per second

CO2 Consumption Reference

(bps = bubbles per second. The Low column uses the 0.5 factors, Medium the 1.0 factors, High the 1.5 factors for both plants and light.)

Cylinder Duration

A standard 5 lb (2.27 kg) CO2 cylinder holds roughly 2,270 grams of CO2. Each bubble is approximately 0.05 mL of CO2 at atmospheric pressure, which weighs about 0.1 mg. Running at 3 bps for 8 hours per day:

Daily usage = 3 × 3600 × 8 × 0.0001 g = 8.64 grams/day Cylinder life = 2270 / 8.64 ≈ 263 days

Always use a drop checker with 4 dKH (degrees of carbonate hardness) reference solution to verify your dissolved CO2 level. The drop checker should turn green (about 30 ppm) during the photoperiod.