Determine Toxic Free Ammonia (NH3)
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Try Koi Toolkit PRO →Understanding ammonia toxicity is critical for koi health. Most standard liquid drop test kits measure Total Ammonia Nitrogen (TAN). However, TAN is made up of two parts: safe ionised ammonium (NH4+) and highly toxic free ammonia (NH3). This free ammonia calculator helps you determine the exact level of toxic NH3 in your pond water.
The toxicity of ammonia in a koi pond is heavily dependent on your water's pH and temperature. As pH and temperature rise, safe ammonium rapidly converts into deadly free ammonia. A TAN reading of 1.0 mg/l might be completely harmless in a cold, low-pH winter pond, but utterly lethal in the middle of summer.
Ideally, your toxic free ammonia (NH3) should always be below 0.02 mg/l. If our calculator warns you that levels are in the danger zone (>0.04 mg/l), you must take immediate action. Stop feeding your koi, perform a partial water change, and consider adding an ammonia binder to temporarily neutralise the toxicity while your biofilter catches up.