Free aquarium CO2 calculator. Calculate optimal bubble rate (BPS) for your planted tank based on volume and plant density. Target PPM recommendations included.
Carbon dioxide management is the single most important variable separating average planted aquariums from world-class aquascapes. Aquatic plants depend on dissolved CO2 for photosynthesis, and in moderately to brightly lit tanks the ambient CO2 from fish respiration is rarely sufficient to support rapid, healthy growth. This calculator translates your tank volume and planting density into a recommended bubble rate (BPS) and target dissolved concentration in ppm, giving you a defensible starting point before fine-tuning by drop checker color and plant response.
The algorithm begins with your net water volume in liters and applies a density-dependent injection coefficient: a heavily planted Dutch or Iwagumi layout requires roughly twice the dissolved CO2 of a low-tech tank with Anubias and Java fern. The resulting BPS recommendation assumes a working pressure of around 1.5 bar through a standard glass diffuser with bubble counter. It also surfaces a target ppm window (15-25 ppm), the threshold for fish stress (around 25-30 ppm), and a danger ceiling above which surface gasping becomes likely. Always cross-check with a drop checker filled with 4 dKH reference solution.
Enter your tank volume and plant density to calculate recommended CO2 dosing (BPS). CO2 is a key factor in plant growth in planted aquariums.
Dose CO2 only during the lighting period and stop 1–2 hours before lights off. CO2 accumulation overnight can sharply lower pH, harming fish.
Monitor dissolved CO2 with a drop checker or test kit. The safe injection target is 15–25 ppm. Above 25 ppm fish may show stress; above 30 ppm can be lethal for sensitive species. If fish gasp at the surface, reduce CO2 immediately.
Plants use CO2 for photosynthesis. In low-light tanks, natural CO2 from fish waste is sufficient. In high-light tanks with dense plants, supplemental CO2 increases growth. Safe target range is 15–25 ppm CO2.
BPS measures CO2 injection rate. 1 BPS = 1 bubble per second. Typical rates are 1-3 BPS for small tanks, 3-5 for medium, 5+ for large tanks. Adjust based on plant growth and CO2 levels.
This calculator uses standard guidelines for CO2 injection. Actual needs depend on plant density, light intensity, and water parameters. Use a CO2 test kit to verify levels.
Options include pressurized cylinders (best for large tanks), DIY yeast systems (budget-friendly), and liquid CO2 (convenient but expensive). Choose based on tank size and budget.
Properly dosed CO2 (15–25 ppm) is safe for fish. Above 25 ppm fish can show stress; above 30 ppm is often lethal for sensitive species. Monitor pH and CO2 levels. Use a drop checker to verify CO2 concentration. Ensure adequate aeration.