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Ammonia is toxic to fish. Exposure to ammonia results in an increase in mucus on the fish. The increased mucus may harbour bacteria and parasites which will cause infection. Gills may also become swollen and both will result in the reduced ability of the fish to absorb oxygen.


Typical symptoms include:

  • Increased mucus layer on fishes mucus membrane.
  • Swollen gills.
  • Fin rot.
  • Flicking against hard surfaces.
  • Gasping at the surface of the water.
  • Inability of fish to maintain its balance in the water.

Ammonia is present in water as a result of the following:

  • Excreta (overfeeding produces more excreta).
  • Decaying, uneaten food.
  • Decaying plant material.
  • Dead and decaying livestock.
  • Filters can become blocked by any of the above thus reducing their efficiency.
  • Filters that are deprived of oxygen can cause ammonia to be returned to the
  • aquarium.

Reduce Ammonia by the following:

  • Reduce feeding.
  • Reduce stocking levels if overstocked.
  • Feed with a good quality food substance.
  • Remove dead and decaying leaves and plants.
  • Clean tank regularly (bi weekly recommended).
  • Clean filters according to manufacturers instructions.
  • Ion Exchange Filter Media such as Activated Carbon, Charcoal and Peat can
  • remove ammonia.
  • Partial water changes.
  • There are two different types of ammonia: Ammonium and Free Ammonia. Ammonium is relatively safe for fish, whereas Free Ammonia is extremely toxic. There is a direct connection to temperature, pH and Ammonia as follows: High Temperature & High pH = High levels of Free Ammonia.
  • Low Temperature & Low pH = Low levels of Free Ammonia. Proprietary kits can be purchased to monitor levels of ammonia.