Aquarium pH/KH/CO2 Calculator
Calculate CO2 level, target pH, and pH drop from KH and pH relationships.
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Model reference bands — not a safety test for fish or invertebrates.
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Aquarium pH/KH/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 x KH x 10^(7 - pH). Enter carbonate hardness in °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 pH drop around 1.0 is a practical upper guideline, but not a rule. Watch fish and invertebrate 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. It assumes carbonate buffering is the main factor. Other acids or buffers from wood, soil, or additives can affect pH, so confirm with real observations.
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