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A browser-based aquarium co2 concentration calculator tool. No data sent to server.

📘 How to Use

  1. Set the pH value using the slider or input field.
  2. Set the KH (carbonate hardness) value to see the result.

Aquarium CO2 Concentration Calculator

-- mg/L

0 20 30 60+

info Results are for reference only. Actual CO2 levels vary with temperature and pressure. Always verify with a drop checker or water test kit in your aquarium.

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Article

Aquarium CO2 Calculator｜Estimate CO2 Levels from pH and KH

This tool provides an instant estimate of the CO2 concentration in your aquarium water based on its pH and carbonate hardness (KH) values. It's designed for aquascapers and planted tank enthusiasts to easily monitor and maintain optimal conditions for plant growth.

💡 Tool Overview

  • Instant Calculation: Automatically calculates the estimated CO2 concentration (in mg/L) as you adjust the pH and KH sliders.
  • Visual CO2 Indicator: A color-coded bar and marker visually represent the CO2 level, allowing you to quickly see if it's in the low, optimal, or high range.
  • Clear Status Feedback: The tool displays a clear status label ("Low," "Optimal," or "High") with a brief description to help you interpret the results.
  • Interactive Controls: Use the intuitive sliders for quick adjustments or type precise values into the input fields for accurate calculations.

🧐 Frequently Asked Questions

Q. What is the ideal CO2 level for a planted aquarium?

A. The generally accepted optimal range for CO2 is between 20-30 mg/L. This concentration promotes robust plant growth and photosynthesis without posing a significant risk to fish and shrimp. Levels above 30-35 mg/L can become stressful or dangerous for livestock. This calculator uses the 20-30 mg/L range as the "Optimal" green zone.

Q. Why does this calculator only provide an estimate?

A. The calculation is based on a pure water system where the pH is influenced only by the carbonate buffer (KH) and dissolved CO2. However, real aquarium water can contain other acids (e.g., from driftwood, substrate, or waste) that lower the pH independently of CO2. This can lead to an overestimation of the actual CO2 levels. For this reason, the result should be used as a guideline and cross-referenced with a drop checker.

📚 The pH, KH, and CO2 Relationship

The relationship between pH, KH, and CO2 is a fundamental concept in aquatic chemistry. When CO2 is dissolved in water, it forms carbonic acid (H₂CO₃), which in turn lowers the pH of the water. KH, or carbonate hardness, represents the water's buffering capacity—its ability to resist these pH drops.

Because these three parameters are interlinked, if you know the values of any two, you can determine the third. This calculator uses the standard formula: CO2 (mg/L) = 3 * KH * 10^(7.0 - pH).

While this chart is an invaluable tool for quick checks, it's highly recommended to use it in conjunction with a CO2 drop checker. A drop checker uses a reagent (like Bromothymol blue) that changes color based on the CO2 concentration in the air bubble inside it, providing a direct measurement that isn't skewed by other acids in the water column. Using both methods gives you the most complete and accurate picture of your tank's CO2 levels.