CO₂ Injection & BPM Calculator

Size your CO₂ injection to reach and hold a target ppm. Enter tank size, current CO₂, diffuser efficiency and outgassing rate. Get the steady “hold” BPM and an optional faster ramp BPM to reach your target in a set time. Includes an estimated CO₂ curve over time and safety guidance for planted tanks.

Tank & Water
Injection & Losses

Recommended Injection

Enter details to calculate steady “hold” BPM, fast ramp BPM and see the predicted CO₂ curve.

Hold BPM (steady)
—
Maintain the target at equilibrium.
Ramp BPM (reach in time)
—
Use until target is reached, then drop to “hold”.
CO₂ Mass Rate @ Hold
—
Approximate dissolved mg/min being added at hold.
Safety Check
—
Flags >30–35 ppm or rapid ramps.

Predicted CO₂ (ppm) vs Time

Curve shows starting at current ppm, using Ramp BPM, then switching to Hold BPM at target.

How This CO₂ BPM Calculator Works

Dissolved CO₂ changes from two main effects: injection (bubbles dissolving into water) and outgassing (CO₂ escaping to air). We estimate bubble mass from bubble volume and convert gas volume to mass (≈1.96 mg per mL CO₂ at STP). We then apply a diffusion efficiency for your diffuser/reactor and an outgassing constant k (/hour). “Hold BPM” maintains a steady target; “Ramp BPM” reaches the target by a chosen time, then you can drop to “hold”.

Recommended Targets & Safety

  • Typical planted tanks: 20–30 ppm during photoperiod.
  • Risk: >35–40 ppm can stress fish and invertebrates; watch for gasping at the surface.
  • Ramps: Increase CO₂ gradually before lights on; avoid large jumps in <30 minutes.
  • Aeration: Gentle surface movement keeps pH/CO₂ swings calmer and livestock safer.

Tuning Tips

  • Measure: Use a reliable drop checker (4 °dKH reagent) and, if possible, a pH/KH method to cross-check ppm.
  • Diffusion: Inline reactors > ceramic diffusers for efficiency; clean diffusers often.
  • Consistency: Use a solenoid to pre-inject 1–2 hours before lights on so CO₂ is stable at peak light.
  • Balance: Match light and nutrients—high CO₂ without macros/micros won’t prevent algae.

FAQs — CO₂ in Planted Tanks

How many bubbles per minute for a 20 gallon?

It varies with diffuser and surface agitation. Start low (e.g., 1–2 BPS), watch the drop checker, and adjust slowly every few days.

What if my fish are gasping?

Reduce BPM immediately, increase surface agitation, and ensure good circulation. Resume slowly once behavior normalizes.

Can I use “liquid carbon” instead?

Liquid carbon (glutaraldehyde) is not gaseous CO₂. It can supplement carbon but doesn’t replicate stable 20–30 ppm CO₂.