Any ammonia above zero in a tank with fish is a warning. At 0.25 ppm, change 30–50% of the water with dechlorinated water at the same temperature and feed less. At 1 ppm or more, change water now and again the next day. Then find the cause: usually an uncycled tank, overfeeding or a dead fish.
What your reading means
0 ppmNormal in a cycled tank
0.25 ppmChange 30–50%, feed less
1 ppm+Urgent: change water now
Common causes
- The tank isn't cycled yet. Normal in the first weeks. See how to cycle.
- Too much food. Feed what fish finish in a minute or two.
- Something died. Check behind decor and plants.
- The filter was cleaned in tap water. Chlorine kills the bacteria. Rinse media in old tank water.
- Too many fish. Check your stocking.
Questions
What are the signs of ammonia poisoning?
Fish gasping at the surface, red or inflamed gills, lethargy, clamped fins. Test right away; you can't see ammonia.
Does a water conditioner remove ammonia?
Some conditioners bind ammonia for about a day, which can buy time, but they don't remove it. Water changes do.
General information, not veterinary advice. Updated November 2026.