Aquarium CO₂ estimates: pH/KH tables and measurement limits
By Richard James · Manufacturer sources checked · 28 October 2026
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Quick answer
A pH/KH table is an estimate based on water chemistry, not a direct CO₂ measurement or a safe injection prescription. Record the method and do not chase a universal pH drop or bubble count.
Why pH alone is not a CO₂ reading
Manufacturer explanations identify CO₂ as one influence on pH, but other acids can also change it. Substrate, botanicals and buffering inputs therefore matter when interpreting an aquarium. JBL’s direct-test instructions even require a blank correction for other acids; follow the full method rather than copying one step.
Before adjusting equipment
| Check | Reason |
|---|---|
| Calibrated pH method and correctly reported KH | Inputs and units affect the estimate |
| Exact diffuser/controller/test instructions | Devices have different methods and delays |
| Circulation, aeration and livestock observations | A target number is not the only relevant evidence |
| Time of sample and equipment settings | Readings from different conditions are not directly comparable |
No universal target or one-pH-drop recipe
A plant category or another aquascape’s target does not establish tolerance for every inhabitant. If animals show respiratory distress after injection, stop increasing CO₂, reduce/stop the supply, increase aeration and obtain prompt qualified aquatic advice. Do not wait for a colour indicator to catch up.
Keep liquid carbon separate
Excel is not injected CO₂. Its volume cannot be entered as a CO₂ concentration. This page supplies no automated gas-dose calculator, off-label controller setting or household test-solution recipe. Read the liquid-carbon limitations and keep the equipment maker’s full instructions alongside the record.
Sources and check scope
- JBL CO₂ table and context
- JBL direct-test method and respiratory-distress guidance
- The 2Hr Aquarist pH/KH discussion
- Seachem Excel identity
Sources checked 28 October 2026. Manufacturer measurement and product identity sources checked; no personalised gas-injection prescription or independent animal-safety assessment. This source check was assisted by AI; it is not an independent human expert or veterinary review. Match the exact pack and consult its manufacturer if directions conflict.