Aquarium CO2 Calculator — pH KH Chart & Bubble Rate Planner
Calculate dissolved CO2 ppm using pH and KH readings, estimate cylinder duration, and plan bubble rates and PAR lighting for low-tech and high-tech planted aquascapes.
Select Live Plants
0 SelectedFlora & Lighting Needs Summary
CO2 Cylinder Lifespan Planner
Refill EstimatorpH-KH CO2 Concentration & Heatmap
Dissolved CO2 is mathematically determined by the equilibrium relationship between pH and Carbonate Hardness (KH). Formula: CO2 = 3.0 × KH × 10^(7.0 - pH).
| pH \ KH | 1 | 2 | 3 | 4 | 5 | 6 | 8 | 10 | 12 | 14 |
|---|
Standard Planted Aquarium CO2 & Lighting Matrix
Bubble rates, 5lb cylinder lifespan, and PAR targets across 10 standard tank sizes.
| Tank Size (Gal / L) | Low-Tech Flora (BPS) | High-Tech Carpet (BPS) | 5 lb Tank Lifespan | Substrate PAR Target | Daily Photoperiod |
|---|---|---|---|---|---|
| 5 Gallon (19 L) Nano | 0.0 (Ambient) | 0.5 BPS (1 bubble / 2s) | ~24+ Months | 40–60 µmol | 6.5–7.0 Hours |
| 10 Gallon (38 L) Standard | 0.0 (Ambient) | 1.0 BPS | ~14–16 Months | 50–70 µmol | 7.0 Hours |
| 20 Gallon Long (75 L) | 0.0–0.3 BPS | 1.8–2.0 BPS | ~8–9 Months | 60–80 µmol | 7.0–7.5 Hours |
| 29 Gallon (110 L) Standard | 0.0–0.5 BPS | 2.5 BPS | ~6–7 Months | 65–85 µmol | 7.5 Hours |
| 40 Gallon Breeder (150 L) | 0.0–0.6 BPS | 3.0–3.5 BPS | ~4.5–5.5 Months | 70–90 µmol | 7.5–8.0 Hours |
| 55 Gallon (208 L) Standard | 0.5 BPS | 4.0 BPS | ~3.5–4.0 Months | 75–100 µmol (Deep) | 7.5–8.0 Hours |
| 75 Gallon (284 L) Standard | 0.8 BPS | 5.0 BPS | ~2.5–3.0 Months | 80–110 µmol | 8.0 Hours |
| 90 Gallon (340 L) Standard | 1.0 BPS | 6.0 BPS | ~2.0–2.5 Months | 90–120 µmol (Deep) | 8.0 Hours |
| 125 Gallon (473 L) Large | 1.5 BPS | 8.0 BPS (Dual Diffusers) | ~1.5–2.0 Months | 90–125 µmol | 8.0 Hours |
| 150 Gallon (568 L) Show | 2.0 BPS | 10.0 BPS (Inline Reactor) | ~1.2–1.5 Months | 100–130 µmol | 8.0 Hours |
Next Steps in Planning
Aquarium Plant Calculator — PAR, CO2 & pH KH Guide.
Planted aquariums require balancing light, carbon dioxide (CO2), and macro/micro-nutrients. If you increase lighting intensity without injecting carbon dioxide, algae will quickly consume the excess energy. The aquarium plant calculator helps you select plants by PAR range, calculate ideal CO2 bubble rates per second, and check dissolved CO2 ppm using the pH KH CO2 chart. Use the planted tank lighting calculator to match your light fixture to your tank dimensions.
PAR Light Requirements by Plant Type
PAR (µmol/m²/s) measures the light intensity available for photosynthesis. Low-light plants (Java Fern, Anubias) thrive at 15–30 PAR. Medium-light plants (Bacopa, Cryptocoryne) need 30–50 PAR. Carpet plants (Dwarf Baby Tears, Monte Carlo) require >50 PAR at the substrate level.
pH-KH-CO2 Relationship
Because carbonate hardness (KH) buffers against pH changes, there is a fixed chemical equilibrium. Injecting CO2 forms carbonic acid, dropping the pH. By measuring pH relative to baseline KH, you can compute dissolved CO2. Optimal is 15–30 ppm. Levels above 40 ppm suffocate fish.
Light-CO2-Nutrient Balance
Increasing light without raising CO2 and nutrients triggers algae blooms — the excess light energy has nowhere to go. All three must be balanced. Low-tech setups rely on ambient CO2 from fish respiration (≈2–5 ppm). High-tech planted tanks inject CO2 to reach 15–30 ppm, matched with high light and regular fertilization.
Planted Tank CO2 Injection & pH KH CO2 Chart
The CO2 bubble rate calculator suggests bubbles per second based on your tank volume and desired CO2 ppm target. Use the pH KH CO2 chart to cross-check dissolved CO2 levels: measure pH and KH, then reference the chart to estimate ppm. Target 20–30 ppm CO2 for high-tech planted tanks and 10–15 ppm for low-tech setups. Deeper tanks lose PAR exponentially — a 60 cm (24 in) deep tank can lose over 50% of surface PAR. The planted tank lighting calculator helps you evaluate PAR at substrate depth.
Frequently Asked Questions
Expert answers to detailed planning questions for this calculator module.
Planted CO2 & Lighting
How many bubbles per second of CO2 does my planted tank need?
CO2 bubble rate depends on tank volume, plant density, and diffusion efficiency. A common starting point is 1 bubble per second per 50 litres for a medium-tech planted tank. Our CO2 calculator determines your target dissolved CO2 concentration (ideally 15–30 ppm for high-tech plants) from your pH and KH readings using the formula: CO2 (ppm) = 3 × KH (dKH) × 10^(7 − pH). The plant planner then recommends a bubble rate in bubbles-per-second based on your plant selection and tank volume.
How do you calculate CO2 ppm using pH and KH?
Dissolved CO2 is calculated using the Henderson-Hasselbalch carbon equilibrium formula: CO2 (ppm) = 3.0 × KH (dKH) × 10^(7.0 − pH). For example, at pH 6.8 and 4 dKH, the dissolved CO2 concentration is approximately 24 ppm.
What is the ideal CO2 level for a planted aquarium?
The optimal CO2 concentration for high-tech planted tanks is 15 to 30 ppm. Levels below 15 ppm limit plant growth and encourage algae, while levels exceeding 40 ppm can suffocate fish.
How many bubbles per second of CO2 do I need?
Bubble rate depends on tank volume, plant density, and diffusion efficiency. As a baseline: a 20-gallon planted tank needs approximately 1 bubble per 2–3 seconds (0.3–0.5 BPS), while a 55-gallon tank requires 1 to 2 bubbles per second. Always monitor drop checkers and pH-KH values when adjusting bubble rates.
What PAR light level do aquarium plants need?
Low-light plants (Java Fern, Anubias) require 15–30 µmol/m²/s PAR at substrate depth. Medium-light plants (Crypts, Stem plants) need 30–50 PAR. High-light carpet plants (Monte Carlo, Dwarf Baby Tears) require >50 PAR and CO2 injection.