Aquarium Water Quality: Ammonia and Oxygen
An aquarium in a Cairo or Giza flat can look perfectly clear while the water inside is toxic. Ammonia is colourless and odourless at low levels and comes from fish waste, uneaten food and respiration through the gills. Owners see one fish die each week and assume disease, when the real number is in the water. This guide explains the nitrogen cycle in simple terms, how to read a test result, what to do immediately when it spikes, and the cleaning mistakes that wipe out beneficial bacteria.
The nitrogen cycle inside the tank
Fish release ammonia through the gills and urine, and this compound burns the gill membranes. Nitrosomonas bacteria convert ammonia into nitrite, which is also toxic, then Nitrobacter converts nitrite into the far less harmful nitrate that is removed by water changes and plants. This cycle needs two to six weeks to stabilise in a new tank.
Any new tank, a filter rinsed under tap water or antibiotics added to the water can kill these bacteria and reset the cycle. That is why ammonia spikes in tanks that are months old, not only in new ones, especially after adding many fish at once or washing the whole filter under the tap.
Signs of high ammonia and nitrite
An affected fish gasps at the surface, hovers near the filter looking for oxygen and becomes lethargic with clamped fins. Gills may look red or brown, eyes can turn cloudy, and appetite drops. In advanced cases the fish swims erratically and then dies, often in the morning because oxygen reaches its lowest level overnight.
Cloudy water is not a reliable indicator: clear water can carry high ammonia, while yellow water may simply be stained by driftwood or decor. Smell is not enough either. A digital meter or a drop test kit is the only way to know the real level and make the right decision.
- Constant gasping at the surface or near the filter outlet.
- Clamped fins and erratic swimming.
- Red or dark gills with loss of appetite.
- Repeated morning deaths after a night without light.
- Cloudy water or surface foam after overfeeding.
How to measure and interpret the result
Test ammonia and nitrite weekly in a stable tank, and daily in a new tank or when deaths occur. The safe level for both is zero, any reading of 0.25 mg per litre calls for an immediate water change, and 1 mg per litre or more is an emergency. Remember that ammonia toxicity increases as pH and temperature rise.
Record pH, hardness and temperature with every test, because a single number is not enough. Use a digital thermometer to track temperature accurately, and test your tap water before use since it may contain chlorine or chloramine. If results are confusing, take a sample to a trusted fish shop or a vet.
The fix and daily prevention
When levels rise, change 30 to 50 percent of the water with dechlorinated water at a similar temperature, cut feeding to a minimum for two days and add strong aeration. Never wash the filter with soap or replace all media at once. Use a starter bacteria or biological booster if the cycle has crashed, and avoid antibiotics in the water unless a vet prescribes them.
For the long term, stock no more than roughly one centimetre of fish per litre of water, and feed only what is eaten in two minutes. Check the filter weekly and rinse the media in tank water, not tap water. Find what you need in our fish supplies and browse more in the shop, remembering that stability matters more than any quick product.
Conclusion
Ammonia cannot be seen or smelled, but it leaves a clear mark on fish behaviour and appetite. Test the water regularly, protect the beneficial bacteria and never medicate before you know the number. A stable tank is cheaper and easier than trying to rescue dead fish.
This article is general guidance and is not a substitute for examining your animal by a licensed veterinarian. In emergencies, contact your vet immediately.
