Ammonia toxicity calculator

This is a freshwater estimate and it does not correct for salt. Check which units your test kit reports in, and follow the product label or a vet's advice before you treat.

T is the temperature in Celsius. This is the Emerson equation, using the 2729.92 constant quoted in secondary sources. It accepts 0 to 50°C (32 to 122°F) and pH 4 to 11.

A reading given as NH3 is 1.216 times the same reading given as NH3-N, so check your kit's manual for which one it uses. The result is shown in mg/L NH3-N.

Below 0.05 mg/L there is no acute concern. From 0.05 to 0.4 mg/L the fish are under chronic stress, and above 0.4 mg/L you should act straight away. Published acute toxicity figures for carp and goldfish vary, but the range starts around 0.9 mg/L. How long the fish are exposed and which species they are both change the risk.

pH often rises through the afternoon. Test nitrite as well, and if your tap water is treated with chloramine, check the replacement water for ammonia. Salt can lower the free ammonia fraction, and this calculation does not correct for that.

For a high reading, do a partial water change, stop feeding and add aeration. Dechlorinate the new water and match its temperature to the pond. Avoid changing the pH quickly.