Aquarium Maintenance - High Nitrite

The number one thing I say to fish keepers is; if the fish look ill test the water  before doing anything else. Water quality is the key to healthy disease resistant fish. Poor water quality if not outright toxic will make the fish more prone to parasites and infections. Most healthy fish carry parasites but it is only when their immune system is suppressed that the parasites are able to take hold. Many aquarium fish are not tolerant of nitrite. Nitrite affects the gills ability to up take oxygen and the fish die of anoxia (lack of oxygen). Click on this link or the picture below you buy an NT Labs test from Amazon UK.

There are various reasons why you would have high nitrites in an aquarium. I will run through the most common causes:

  • New tank syndrome.
  • Over stocking / under sized filtration.
  • Over feeding.
  • Poor filter maintenance.
  • Poor general maintenance.


New Tank Syndrome; It takes time to mature an aquarium. Bacteria that ‘feed’ off the organic waste produced by the livestock build up slowly. They also grow in proportion to the ‘food’ available. A new tank should be left for a week or so before fish are added so to allow the bacteria to build up. A bacteria starter can be added to help this process. The first stocking should be of a small number of hardy fish such as Golden Barbs. Then closely monitor the water and make sure that no ammonia or nitrite is present before adding any more fish. 

Over Stocking / Under Sized Filtration; Filters are only able to cope with so much. When buying a filter make sure it is not only suitable for the size tank you have but it is able to handle the size and the numbers of fish you wish to keep. AND remember fish grow so check out their maximum size before adding them to your aquarium.

Over Feeding: A common problem. Time and time again customers say that their fish always look hungry. Fish will eat almost all day long, resist the urge. Filters are only able to cope with so much. As a rule feed once a day, about a pinch is all that is needed and watch your fish. You can tell a lot about fish at feeding times. If over a week or so the fish are looking thin then up the feeding, if fat reduce.

Poor filter maintenance; Filter media (foams etc.) must always be cleaned using water from the tank. Tap water contains chlorine and if used would kill off ‘friendly’ bacteria which break down fish waste. Ammonia is produced by the fish and bacteria in the filter break it down to nitrite and then another strain of bacteria break it down to nitrate.

Poor general maintenance; Clean your filter regularly. Filter bacteria require a regular flow of well oxygenated, aquarium water and a surface area on which to ‘live’. If the filter slows and the surface of media becomes clogged then the bacteria start to die off reducing the breakdown of toxins causing a nitrite and even an ammonia spike. Also undertake regular water changes and gravel cleans, keep the substrate clear of waste material.


Helpful tips;

  • Salt is useful as it detoxifies nitrite however it does also reduce the amount of oxygen that water can ‘hold’. When using salt make sure the water is well aerated. Some fish can also be sensitive to salt. Always follow the manufactures instructions on dose rates. 
  • Good quality bacteria boasters can help to increase bacteria numbers. 
  • Stop feeding until the problem is fixed. If it stops going in one end far less comes out the other!
  • Keep checking your water.
Amazon link for Easy Life Filter mediaLiquid Filter Medium from Easy Life can be used to increase bacteria numbers when maturing an aquarium or when you have water quality problems. Click on picture for Amazon UK link.


Always test the water before doing anything else!




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