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Author: Dr. L.E. Freese

Ammonia, Nitrite and Nitrate

To be able to understand the interactions of ammonia, nitrite and nitrate one must understand the nitrogen cycle, which is summarised in the drawing below.

When setting up a new aquarium it is important to allow the tank to mature before you stock it with fish.

The new tank is a sterile environment, which does not contain the nitrifying bacteria that are necessary to breakdown metabolic waste products produced by the fish.

The necessary bacteria are found everywhere even in the air. As soon as there is ammonia present in the water, the bacteria that utilise ammonia i.e. Nitrosomonas establish a colony in the substrate of the biological filter, provided there is an adequate supply of oxygen and surface area for the bacteria to adhere to.

There are a number of ways to introduce ammonia into the tank:

• Add a flake of food each day and allow it to decompose
• Plants in the tank to provide debris
• Add 1 or 2 hardy fish that provide ammonia in their excrement (Hardy fish are fish that are tolerant to high levels of ammonia) this method is not the best as the fish are exposed to dangerous levels of ammonia and they could die.

With the spike of ammonia, Nitrosomonas bacteria have enough "food" and convert it to nitrite. This leads to a spike in nitrite levels and the second set of bacteria Nitrobacter are able to form colonies in the biological filter and the substrate where the conversion of nitrite to nitrate takes place.

It is important to measure the levels of ammonia, nitrite and nitrate in the water. When nitrates are produced the tank is mature enough for the gradual introduction of fish. This phase of establishing the tank can take 2-6 weeks and in extreme cases up to 12 weeks.

Graph showing the spikes of ammonia and nitrite and the build up of nitrate

Ways to shorten the time for maturation:

• Borrow an insert (foam or floss) from an established tank

• Collect substrate from an established tank
• Connect your filter to an established tank for a week

The problem with doing this is that you might end up with unwanted bacteria and diseases in your new tank, therefore be very careful about the condition of the established tank before using anything from it.

When the aquarium is not allowed to mature and too many fish are added, the tank succumbs to " new tank syndrome". In other words the fish will suffer from acute ammonia and nitrite intoxication and the possibility of fish deaths is high. If you notice that your fish are not healthy or that some fish are dying it is best to either remove the fish from the tank or to reduce the ammonia and nitrite levels in the tank. The methods of doing this are discussed below.

Ammonia

What is ammonia?

Ammonia is a metabolic by product from fish. Fish excrete ammonia from their gills and with their faeces. When faecal matter breaks down more ammonia is released.

Ammonia is formed when proteins and amino acids are metabolised and therefore if fish are overfed, the left over food increases the ammonia concentration in the water. Another source of ammonia is the decomposition of waste matter (dead plants, fish, snails etc.).

There are 2 forms of ammonia in the water, ionised ammonia (NH4) and unionised ammonia (NH3) which is the toxic one of the two. The proportion of NH4 to NH3 depends upon the salinity, temperature and pH of the water.

What effect does ammonia have on my fish?

Ammonia is highly toxic to fish; even small amounts increase the stress levels for fish.

The effects may be summarised as follows:

• Increased gill rate and gasping
• Increased mucous production
• Reddening of the skin
• Hyperactivity and nervous behaviour
• Erratic swimming and twitching

The standard test kits that are available test the total ammonia (NH3 + NH4) levels in the tank and in an established system the reading should be zero.

Certain species are more tolerant to ammonia than others and this presents a problem when trying to determine the toxic level of ammonia. Levels of toxic ammonia (NH3) must be kept at levels below 0.02mg/L.

To be able to determine the level of NH3 in a tank, the total ammonia readings must be converted to NH3 based on the temperature and pH of the water. (Test kits should have the conversion table included in the kit.)

Therefore if the test kit has a total ammonia reading of 1ppm with the temperature of 26°C and a pH value of 7, the level of NH3 is calculated as follows: (See table 1 for percentage values)

The level of NH3 is below the toxic level, but it should be monitored to see that it does not rise.

If the temperature stays the same but the pH is 8.4

Hence we can see that the NH3 is at a toxic level and this has to be brought down immediately.

Table 1: Percentage of total ammonia in the un-ionised form (NH3) at differing pH values and temperatures.

The following steps should be taken to rectify the problem.

1. Stop feeding the fish for at least a day then gradually increase the amount of food given
2. Do a partial water change (10-25%) once a day until the levels are down
3. Ensure that the water flow to and from the biological filter is not blocked
4. Check that the aquarium is sufficiently aerated as oxygen is required for the nitrifying bacteria to break down the ammonia into nitrite
5. Make sure that your tank is not overstocked
6. Use an ammonia reduction additive in severe cases

Nitrite

What is nitrite?

Nitrite (NO2) is an oxidised form of Nitrogen and is formed when ammonia is oxidised by nitrifying bacteria (Nitrosomonas).

Nitrite is toxic to fish, only slightly less than ammonia. Nitrite leads to a condition known as "brown blood" due to the brown colour of the gills of the affected fish.

Nitrite has the ability of entering the fish’s blood stream and it oxidises the haemoglobin into methaemoglobin, which is not as efficient at transporting oxygen. Therefore fish react as if there is not enough oxygen in the water

• Come to the surface and "gulp" air
• Increased gill movement and gasping
• Lethargy

Fish may die within hours or days.

What levels of nitrite are toxic?

Some fish are more sensitive to nitrite levels than other species and therefore it is best if the level of nitrite is maintained at zero. Any levels above 0.1mg/L should be regarded as toxic and the problem needs urgent attention.

How do I reduce the nitrite in my tank?

The following steps should be taken to rectify the problem.

1. Stop feeding the fish for at least a day then gradually increase the amount of food given
2. Do a partial water change (10-25%) once a day until the levels are down
3. Ensure that the water flow to and from the biological filter is not blocked
4. Check that the aquarium is sufficiently aerated as oxygen is required for the nitrifying bacteria (Nitrobacter) to convert nitrite to nitrate

Make sure that your tank is not overstocked

Nitrate

What is nitrate?

Nitrate (NO3) is formed when nitrobacter bacteria oxidize nitrite (NO2).

Plants and algae assimilate nitrate and in this way remove it from the water. Normally when there is an unusual outbreak of algae in the tank this signals an abundance of nitrate.

Nitrate is the least toxic of the elements of the nitrogen cycle and the effects on fish are normally due to long term exposure.

Some of the effects can be summarized as follows:

• Poor growth
• Loss of appetite
• Lethargy
• Chronic stress
• Reluctance to breed
• Increase in gill rate and gasping
• General ill health
• Delayed wound healing
• Clamped fins

Nitrate levels should be kept below 25mg/L although levels of up to 100mg/L have shown to be non-toxic to fish. This is due to the fact that fish acclimatise to high levels of nitrate, if the change is sudden, the fish suffer from nitrate shock.

Toxicity of nitrate is also determined by the availability of oxygen, if there is inadequate oxygenation, fish are more sensitive to nitrate than when the oxygen level is adequate.

The level of nitrate in the water is normally used as an indication of water quality. The higher the level the worse the quality of the water.

Doing a 30% water change once a week prevents nitrates levels from reaching an unwanted level.

The following steps should be taken to rectify the problem.

1. Reduce the amount and frequency of food given
2. Do a partial water change (10-25%) once a day until the levels are down to 20mg/L
3. Ensure that the water flow to and from the biological filter is not blocked
4. Check that the aquarium is sufficiently aerated
5. Make sure that your tank is not overstocked
6. Increase the lighting to promote green algae growth
7. Add plants to the aquarium

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