Aquarium pH & CO2 Calculator

Calculate CO₂ levels, target pH, and pH drop based on proven KH/pH relationships.

Step 1
What do you want to calculate?
Tip: For most users, CO₂ Level Check is the default. Target pH and Drop Helper are planning/diagnostics tools.
Step 2
Inputs
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Step 3
Result
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INFO
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    Advanced analysis model
    Drop checker: best with a 4 °dKH reference solution. Response time is often 30–120 minutes.
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    FAQ
    Aquarium pH & CO2 Calculator FAQ
    How do you calculate CO₂ from KH and pH in an aquarium?
    A common planted-aquarium estimate is: CO₂ (mg/L) = 3 × KH × 10^(7 − pH). Enter carbonate hardness (KH, °dKH) and measured pH to estimate dissolved CO₂.
    What is a good CO₂ level for a planted aquarium?
    Many planted aquariums aim for about 20–30 mg/L CO₂. Lower values can limit growth, while higher values can stress fish if oxygenation is poor. Stability matters most.
    How safe is a 1.0 pH drop with CO₂ injection?
    A ~1.0 pH drop is a practical upper guideline, but not a rule. Watch livestock behavior, ensure good oxygenation and circulation, and increase CO₂ gradually.
    Why does CO₂ lower pH in aquariums?
    CO₂ dissolves into water and forms carbonic acid, which lowers pH. Higher KH buffers this effect, so pH changes less at higher carbonate hardness.
    How accurate is a KH/pH CO₂ calculator?
    The KH/pH method is an approximation. Other acids or buffers (for example from wood, soil, or additives) can affect pH and reduce accuracy. Treat the result as an estimate.

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