CO₂ Calculator for Planted Tanks
Dial in your planted tank: get a starting bubble rate for your tank size and see how long your CO₂ cylinder will last.
Calculate CO₂ bubble rate
How CO₂ dosing works
Injected CO₂ is the single biggest upgrade for a high-tech planted tank. Most aquarists target around 30 ppm of dissolved CO₂, measured with a drop checker that turns green at the right level.
This calculator uses two practical rules:
- Bubble rate ≈ 1 bps per 15 gallons of water — a safe starting point, rounded to the nearest 0.5 bps.
- 1 bps consumes about 25.2 g of CO₂ per day — so a 5 lb (2,270 g) cylinder lasts roughly 90 days at 1 bps. Cylinder life = weight ÷ (bps × 25.2 g/day).
CO₂ tips
- Start CO₂ 1–2 hours before lights-on so levels are stable when plants start photosynthesizing.
- Use a drop checker — bubble counters vary between brands, but the drop checker color doesn't lie.
- Too much surface agitation drives CO₂ out of the water; aim for a gentle ripple, not splashing.
- Watch your fish: gasping at the surface means too much CO₂ — dial it back immediately.
Frequently asked questions
What is a good bubble rate for a planted tank?
Start near 1 bps per 15 gallons (a 30-gallon tank starts around 2 bps), then adjust until your drop checker is green at lights-on.
How long will my CO₂ cylinder last?
Divide the cylinder weight in grams by (bps × 25.2). A 5 lb cylinder at 1 bps lasts about 90 days; at 2 bps about 45 days.
Do I need CO₂ for low-light plants?
No. Anubias, java fern, crypts and mosses grow fine without injected CO₂. CO₂ is for medium-to-high light setups and demanding species.
Can CO₂ harm my fish?
Yes, at high levels. Keep the drop checker green (not yellow) and watch for gasping. A solenoid on a timer shuts CO₂ off at night when plants don't use it.