How much CO2 is in one bubble?

A standard aquarium bubble counter bubble is roughly 0.0001 g of CO2 (about 0.05 mL at the gas density of CO2). This tool uses that conversion, so 1 bubble per second is about 8.6 g per day if the system runs continuously.

Should I run CO2 24 hours a day?

Most planted-tank keepers run CO2 only during the photoperiod, typically 8 to 10 hours, switching it off at night when plants do not photosynthesise. Set the daily on-hours field to match your timer for an accurate estimate.

Why is my real-world duration different?

Bubble size varies between diffusers and counters, solenoid ramp-up wastes a little gas, and regulators leave residual pressure that cannot be used. Treat the estimate as a planning figure and order a refill before the cylinder runs fully dry.

What size cylinder should I buy?

Match cylinder size to how often you want to refill. A small 95 g cartridge may last a nano tank weeks but a large display tank at high injection empties it in days, so larger tanks usually justify a refillable 1 to 2 kg bottle.

How do I find grams per day directly?

Weigh the cylinder on a kitchen scale a week apart; the difference divided by the days is your real grams-per-day. Enter that in the grams mode for the most accurate duration, since it captures your exact diffuser efficiency.

CO2 Cylinder Duration Calculator

A CO2 cylinder on a planted aquarium drains slowly enough that it is easy to be caught out by an empty bottle. This calculator turns your injection rate into a grams-per-day figure and tells you roughly how many days of CO2 you have left, so you can order a refill in good time.

How it works

CO2 usage is mass over time. The tool supports two input modes. In bubble mode it converts bubbles per second to grams per day using a standard bubble mass and your daily on-time:

grams/day = bubbles_per_sec × 0.0001 g × 3600 × on_hours
days left = remaining_grams / grams_per_day

In grams mode you enter a measured grams-per-day directly and the tool simply divides remaining cylinder mass by it. Measuring the real weight loss over a week is the most accurate method because it captures your specific diffuser and bubble size.

Example and tips

A 500 g cylinder injecting 2 bubbles per second for 9 hours a day uses about 2 × 0.0001 × 3600 × 9 = 6.5 g per day, so it lasts roughly 77 days. Run CO2 only during the photoperiod via a solenoid and timer — plants cannot use it in the dark and continuous injection can crash pH overnight. Order your refill when the estimate drops below a week, since regulators leave a little unusable residual pressure and real bubble sizes vary.