Koi Pond Ammonia (NH3) Calculator
Free Water-Quality Calculator
Estimate un-ionized ammonia (NH3) from TAN, pH, and temperature
Total ammonia exists mainly as ammonium (NH4+) and un-ionized ammonia (NH3). Higher pH and temperature shift a larger fraction toward NH3, the form generally associated with greater toxicity to fish.
1. Ammonia measurement
This calculator expects TAN reported as nitrogen (NH3-N + NH4-N). Check your test-kit documentation before entering a value labeled only “ammonia.”
2. Pond conditions
Estimated un-ionized ammonia
This converts NH3-N to NH3 by molecular mass. Keep the reporting basis straight when comparing a result with another reference.
Ammonia equilibrium formula
The calculator uses the freshwater equilibrium relationship commonly attributed to Emerson and used in EPA ammonia guidance.
pKa
0.09018 + 2729.92 ÷ (273.2 + T°C)
NH3 fraction
1 ÷ (1 + 10(pKa − pH))
NH3-N
TAN × NH3 fraction
Read the units before using the result
“Ammonia” is not always reported on the same basis. This calculator expects total ammonia nitrogen in mg/L as nitrogen. Some hobby tests or references may instead report ammonia in a different chemical or mass basis. If the units do not match, do not compare the numbers directly.