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Ammonia In Ponds and Aquariums

Ammonia In Ponds and Aquariums and How to Lower It

Ammonia in ponds and aquariums is a common problem. Ammonia stress and poisoning is often the number one cause of fish illness and deaths when setting up new aquariums, small ponds and quarantine tanks.  This is often referred to as ‘New Tank Syndrome’. It is not usually as common a problem in new larger ponds because the ammonia is diluted in the larger volume of water and doesn’t reach toxic levels. Ammonia stress can also occur in well established ponds for a variety of different reasons. It also usually the first step in a parasite or bacterial outbreak because it stresses and weakens the fish making them more vulnerable to pathogens in the water.

Luckily, koi and goldfish as well as many aquarium fish are quite resilient and can withstand low ammonia levels for a few days without any adverse effects. But ammonia levels can rise to dangerous levels quite quickly and lead to serious fish health problems and deaths.

 What is Ammonia and Where Does it Come From?

Ammonia is the primary waste product of fish. It is excreted mainly through their gills and to a lesser extent as urine. It can also come from decaying plant matter, dead algae or dead fish or other animals in the pond.

 What are the Symptoms of Ammonia Stress?

The first signs of ammonia stress are often the behavior of the koi or goldfish. In ponds or aquariums with high ammonia levels, fish will often become less active and hang at the surface of the water gasping near waterfalls or filter returns.

Other signs include:

  • sitting on the bottom
  • loss of appetite
  • fins clamped close to their body
  • excess mucous slime coat


A closer inspection of the fish usually shows reddening of the skin and damage to their gills.

How Does Ammonia Affect Fish?

Even low levels of ammonia, below 0.25 ppm (parts per million), can suppress the immune system and make the fish more susceptible to bacterial and parasitic infections.

High levels of ammonia, 1.0 ppm or more, have a caustic effect on a fish’s gills with sudden and dramatics effects. Higher levels of ammonia will ‘burn’ the gills and actually cause swelling and even serious damage to the structure of the gills. Fish not only use their gills to breath, but also for waste excretion an osmoregulation (the balance of water and salts in the body). This drastically reduces the ability of the gills to function properly and also makes them more susceptible to infection. It only takes a few days of high ammonia levels to harm fish.

What Causes Ammonia?

Ammonia is present in all ponds and aquariums, but usually in minute amounts. That is because in an established well functioning pond or aquarium, toxic ammonia is converted into relatively harmless nitrates by beneficial bacteria through a series of biological steps. This process of converting ammonia into nitrates is called The Nitrogen Cycle, also known as ‘The Cycle’ or ‘Cycling a Tank’.

The Nitrogen Cycle

The Nitrogen Cycle - Ammonia in Ponds and Aquariums

Here’s what happens with ‘The Cycle’ when you set up a new pond or aquarium. You add some fish, begin feeding them and everything is great. The fish immediately start producing ammonia waste and it starts to build up in the water.

  1. As the Ammonia level increases (follow the RED line in the graph above) beneficial bacteria called Nitrosomonas begin to use this as a food source and convert it into Nitrites. As these bacteria multiply, they are able to consume more and more ammonia so that eventually ammonia levels will drop to almost zero.
  2. Nitrites (the ORANGE line) are less toxic to fish than ammonia, but are still very dangerous at higher levels and can kill fish. As the Nitrite levels increase, Nitrobacter bacteria begin to convert the Nitrite into less harmful Nitrates (the GREEN line). As the Nitrobacter bacteria multiply, Nitrites will be also be converted immediately into nitrates so that the Nitrite level in the water will be virtually zero.
  3. Nitrates will accumulate in a pond or aquarium that has no plants or algae. Nitrates are not broken down by bacteria like ammonia and nitrites. Although Nitrate does not directly affect fish like ammonia or nitrite, chronic high levels (over 50 ppm) can start to weaken fishes immune systems, making them more vulnerable to infections and parasites. To reduce Nitrates and maintain healthy levels in an aquarium, regular partial water changes (10% to 20%) should be performed. In a pond, nature has a way of taking care of nitrates – ALGAE! Algae and plants feed on nitrates, so if you don’t want pea soup green water or string algae overtaking your pond, add lots of plants to consume the nitrates. Check out our Clear Water Plants page for more tips.


The process above is completely natural, if you are patient when you first start up a pond or aquarium and don’t add too many fish during the first month, you shouldn’t have any major water quality problems or sick fish. Problems usually occur when enthusiastic hobbyist add too many fish too fast to a new aquarium and don’t check their water quality.

In established systems, ammonia levels can also become dangerously high for a variety of reasons. Inadequate filtration or circulation, overfeeding, overstocking, spawning, extended power outages, killing a lot of algae and not removing it from the pond and treating with medications can all result in elevated ammonia levels.


How to Prevent High Ammonia Levels

  • Check water quality regularly
  • Have adequate (or more than adequate) filtration and circulation
  • Don’t overstock your system with fish
  • Don’t overfeed your fish
  • Be patient when starting a new system


What Is Considered a Safe Level of Ammonia?

Other than in a new system, Ammonia levels should always be zero. The presence of any ammonia in an established pond or aquarium should be a sign that something is amiss and should be investigated. Ammonia levels above 0.25 ppm should be a concern, anything above 1.0 ppm should be acted upon immediately.

What To Do If I Have High Ammonia Levels?

If you have high ammonia levels, above 1.0 ppm, the first thing to do is a partial water change. How much of a water change and how often to change water depends on the levels. 20% to 30% water changes daily should be adequate to help lower the ammonia levels. In this situation, check your water quality daily, or even twice a day with a Test Kit. If the ammonia levels are above 5.0 ppm, you could increase the amount of water that you change, but extra care must be taken not to shock the fish. Any time you perform a water change, always use a Dechlorinator to remove chlorine and chloramines if you are on town water, always try to make sure the water you are adding to the pond is the same temperature as the pond water (especially if you are doing a large water change).

Add Beneficial Bacteria to your pond or aquarium. There are several good products like Nite-Out II, AmmoniaFix, or Microbe Lift PL that help to establish or restore the beneficial bacteria in your system. In ponds, it is always a good idea to get a head start in the spring by adding Cold Water Beneficial Bacteria that are designed to perform in cold water temperatures.

Ammonia Remover additives are also effective at binding up toxic ammonia so that they don’t harm the fish. The resulting ‘bound’ ammonia is then removed naturally by the beneficial bacteria.