Tools you might need next
Calculate aquarium water volume in gallons and liters for rectangular, bow-front, cylinder, and corner tanks including substrate and displacement.
Check tropical fish compatibility for community tanks by temperament, tank size, water parameters, and schooling needs before adding new species.
Calculate aquarium heater wattage from tank volume, room temperature, target water temperature, and desired heat-up time for stable tropical temps.
Dissolved CO2 correlates with pH and KH via the carbonate equilibrium. At known KH, measure pH drop from CO2 injection to estimate ppm.
CO2 (ppm) ≈ 3 × KH × 10^(7 − pH)Planted tanks target 20–30 ppm CO2 for optimal photosynthesis. Below 10 ppm limits plant growth; above 35 ppm risks fish stress especially overnight when pH drops.
Target: 20–30 ppm CO2Calibrate bubble rate by measuring pH drop over 1–2 hours after injection starts. Typical rates: 1–2 bubbles/sec per 50 gallons, adjusted by diffuser efficiency and surface agitation.
Start rate ≈ (Tank gallons / 50) × 1 bps; adjust to pH/KH targetUpdated: July 2026
Target 25 ppm CO2 requires pH ~6.6 at KH 4 (from ~7.4 without CO2). Start at 1 bubble/sec, measure pH after 2 hours, adjust until stable at 6.6 before lights on.
Larger volume needs 2–3 bubbles/sec with inline diffuser. KH 3 means pH target of ~6.5 for 25 ppm. Use drop checker as secondary confirmation — green indicates ~30 ppm.
Without injection, Excel or similar provides ~5–10 ppm equivalent. Not a substitute for high-light CO2 but sufficient for low-tech plants at 1–2 ml per 10 gallons daily.
Bubble size varies enormously between diffusers and regulators. Use pH/KH measurements or a drop checker to verify actual CO2 levels, then note your bubble rate as a reference.
Overnight CO2 injection drops pH to dangerous levels when plants stop consuming CO2. Always use a solenoid valve on a light timer.
Stable CO2 levels are critical for planted aquarium health and fish safety. This calculator estimates injection rates from tank volume, current and target pH, KH (carbonate hardness), and bubble count to maintain 20–30 ppm dissolved CO2.