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Cycle Chemistry
NH3 vs NH4+ (Ammonia Chemistry)
The critical distinction between toxic un-ionised ammonia (NH3) and less toxic ionised ammonium (NH4+) - the ratio depends on pH and temperature.
Unit: ratio Code: NH3_NH4
📖 Overview
Test kits measure total ammonia (NH3 + NH4+). But only the un-ionised form (NH3) crosses gill membranes and poisons fish. The proportion of NH3 rises sharply with pH: at pH 7 nearly all ammonia is safe NH4+; at pH 9 as much as 30% is toxic NH3. This is why the same measured ammonia concentration is deadly in an African cichlid tank and merely stressful in a discus tank.
❓ Why It Matters
A 0.5 ppm ammonia reading is emergency in a high-pH marine tank, moderate concern in a soft-water freshwater tank.