High Ammonia in Fish Tank: Emergency Fix

Do this first

Safe target: 0 ppm ammonia; readings above roughly 0.25 ppm threaten most freshwater fish.
Emergency steps: Large temperature-matched water change (~50%), stop feeding, remove uneaten food, confirm filter flow.
Root causes: Uncycled or crashed biofilter, overcrowding, overfeeding, dead livestock hiding in decor.

Ammonia burns gills quickly. Visible distress often lags chemistry, especially in hard water.

Corrective order

Test ammonia, nitrite and nitrate to see whether biofilter stalled.
Repeat partial changes while dosing dechlorinator to spec.
Increase gentle surface movement for oxygen—not hurricane flow.
Pair husbandry tweaks with stocking checks inside the free aquarium stocking calculator.

Anchor long-term fixes in understanding the nitrogen cycle; emergency binders assist but never replace colonies.

Browser calculator stays free. The app only matters if you want several tanks, photos, and test history on your phone.