How to Lower Nitrite in a Aquarium Fish Tank Safely

The Fastest Way to Lower Nitrite

There should be no measurable nitrite level in a healthy aquarium. If there is nitrite present and the fish are stressed, fast and cautious actions are required to avoid further aggravation of the situation.

Perform a Partial Water Change

The first step would be changing 30%-50% of water with the use of conditioned water with a temperature similar to the water in the aquarium. Half of the water changed should result in approximately halving the nitrite level.

Before adding new water:

• Remove chlorine and chloramine;
• Maintain a similar temperature.
• Test new water on nitrites whenever possible;
• Do not cause rapid changes in pH, hardness, and salinity levels.

After changing the water, let it flow in the aquarium and then test the nitrite level again. In case the nitrite is still present or the fish are having problems, repeat the process of partial water change.

Changing water removes nitrite rapidly, but it does not fix the biological filtration of the aquarium.

Increase Aeration and Surface Movement

Place an air stone into the tank, change the position of the filter output, or add more turbulent activity at the surface level. Increased water agitation will help to exchange gases better and to have more oxygen for the fish and the bacteria in the filter.

Nitrites affect the transportation of oxygen by the blood of the fish. Therefore, the fish may demonstrate symptoms typical of lack of oxygen in the aquarium even if the water is well-aerated: the fish may gasp, breathe quickly, or stay near the filter output.

Aeration is not a physical method of removing nitrites from the tank. Nevertheless, it helps the stressed fish and the oxygen-using bacteria, which break nitrogen waste products.

Reduce the Amount of Food

Every fish meal will contribute to the nitrogen waste in the aquarium. The fish produce ammonia after they have digested their food, and the uneaten food and other organics decompose and also generate ammonia.

Healthy adult fish should be able to withstand a short period of fasting or reduction in the size of a meal. Take out the uneaten food to prevent its decay.

Fry, weak fish, and fish that are specialists in their feeding requirements may need another solution. The goal is to reduce the creation of wastes for a limited period without denying the fishes of their nutritional requirements.

Keep the Filter Running

The filtration unit should always be left on when the nitrite levels soar. Inspect the intake, impeller, tubing, and the filter media to ensure that there is unrestricted flow through the system.

When your filter is excessively clogged, rinse the reusable filter media in water taken out of the tank. Avoid washing the established media in untreated tap water, and avoid replacing all the sponges and cartridges at once.

Beneficial bacteria exist on the media, substrate, ornaments, plants, and other materials underwater. Too much removal of established materials may harm the nitrogen cycle process and worsen the nitrite problem.

The Process Behind a Nitrite Spike

Nitrite is formed during the intermediate stage of the aquarium nitrogen cycle:

Fish waste and decaying material → Ammonia → Nitrite → Nitrate

The first type of bacteria changes ammonia to nitrite. The second type changes nitrite to nitrate. Under ideal conditions, both reactions occur fast enough for ammonia and nitrite not to be detectable in an aquarium.

The formation of a nitrite peak occurs because the aquarium produces more nitrites than the biological filter is able to oxidize. This situation is frequently encountered when the filter is either new, damaged, overloaded, poorly aerated, or exposed to untreated water.

Nitrite enters the body of the fish via the gills and inhibits the process of oxygen transportation by the bloodstream. Serious nitrite poisoning can lead to the development of a serious condition called brown blood disease.

Common Causes of High Nitrite

An Aquarium That Is Still Cycling

The newly installed aquarium lacks an adequate amount of bacteria capable of processing the whole quantity of fish waste. The level of ammonia usually becomes elevated first, and then nitrite becomes evident due to the efforts of the first group of bacteria.

It might take several weeks for a biological filter to become mature. In this case, frequent testing and feeding become crucial in particular when there are some fish in the aquarium already.

Sudden Increases in Fish or Feeding

Adding multiple fish at once will lead to a rapid increase of waste added to the water. In this case, the filter requires some time for development of more bacteria able to cope with increased load.

Overfeeding results in a similar situation because an increased amount of fish waste is created in this case, and additionally, uneaten food decomposes and adds stress to the process.

Excessive Filter Cleaning

Most owners of aquariums change filters, replace all cartridges, clean the whole substrate, and make water changes in one day. Even though the tank looks cleaner, such a practice will kill too many bacteria.

This may result in a miniature cycling where either ammonia or nitrite appears in the aquarium that was stable earlier.

Untreated Tap WaterS+UR/

Tap water usually consists of chlorine and chloramines. These additives help in making the water free from harmful microorganisms; however, they may be detrimental to the good bacteria in the aquarium filter.

Always use a suitable conditioner on tap water before putting it in the aquarium or biological media.

Medication or Chemical Exposure

Medication, certain cleaning products, and chemical solutions can hinder the functioning of the biological filtration system. An increase in nitrites during or after medication use can be a sign of problems with the bacterial population.

Test for ammonia and nitrite levels in your tank whenever you add any medications to your main aquarium tank.

Filter Shutdown or Power Failure

The nitrifying bacteria require the presence of oxygenated water. Failure of the pump, blockage of intake, power failure, and lack of circulation in the canister filter may result in a lack of oxygenation.

Reactivating the biological filter will increase the water flow, but the biological activity might not return straight away.

Low Oxygen or Depleted Alkalinity

The nitrification cycle relies on sufficient amounts of oxygen and carbonate alkalinity. Limited oxygen or alkalinity means that the bacteria responsible for changing nitrites into nitrates will not function properly.

The nitrification process slowly depletes bicarbonates and results in reducing alkalinity and pH. If the level of nitrites does not drop despite regular maintenance, it is necessary to test the pH and alkalinity levels in the water.

A Practical Nitrite Recovery Plan

Day One

• Take the readings of nitrites using a new water sample.
• Measure nitrites in the source water.
• Carry out a 30% – 50% conditioned water exchange.
• Improve aeration and agitation on the surface of water.
• Reduce feeding or stop feeding altogether.
• Clean the filter from clogging or insufficient water flow.
• Check ammonia, nitrite, nitrate, pH, and water temperature.

The Following Days

Ammonia and nitrite need to be tested daily until they both drop to zero. Do a partial water change every time when there is nitrite detected again.

Feed the fish only a little food, remove excess waste, and keep the filter in operation. Don’t add any more fish or media to the filter and do not add any chemicals to the aquarium.

It is possible that a new aquarium will take a few weeks to stabilize itself, while an established aquarium experiencing a slight problem with its filters will take just a few days, depending on the temperature, the oxygen content in the water, alkalinity, and condition of the filters themselves.

After Nitrite Returns to Zero

Testing should continue for a few more days even after the first day that shows zero results, because one good result does not mean that the filter is able to handle the amount of food and waste products created in the aquarium.

Gradual return to normal feeding practices should be undertaken only when there is no further rise in ammonia and nitrite levels.

Safe Use of Salt During Nitrite Exposure

Chloride is capable of reducing the intake of nitrite through the gills of the freshwater fish due to the fact that chloride and nitrite compete in their uptake by the gills; thus, using carefully measured salt may help in protecting freshwater systems from nitrite.

But there are some things you must consider before using salt in your aquarium:

• It doesn’t eliminate nitrite from water.
• It doesn’t fix or replace biological filtration.
• Not all freshwater fish can tolerate salt.
• Plants, shrimp, snails, and other invertebrates may be sensitive to it.
• Salt stays in the tank until it’s removed during water changes.
• Untested amounts of salt will cause more stress.

Amounts of salt calculated for ponds or even professional fish systems are not always appropriate for a combined aquarium with various fishes. Species of fish, testing units, amounts of chloride, and even water chemistry will differ and require different quantities.

Use salt only after you’ve checked the tolerance of each living creature in your tank. Partial water changing, increasing oxygenation, limiting food, and recovering filters should be the primary way of dealing with the problem.

Test Kit Units That Can Cause Confusion

Nitrite readings of aquarium test kits can either be given as NO₂ or as nitrite-nitrogen (NO₂-N). These readings refer to the same compound; however, their numeric readings are not alike.

The following formula can help:

NO₂ concentration = NO₂-N concentration × 3.3

In other words, a NO₂-N reading of 0.2 mg/L is equal to 0.66 mg/L NO₂. Always check the test kit instruction manual prior to comparing your results with any other source.

Another factor that determines the safe level of nitrite in water is the type of fish. Fish have different degrees of sensitivity to nitrite. Factors such as water chemistry, chloride concentration, age, health, and stress affect sensitivity to nitrite. The safe level of nitrite for an adult fish tank is 0 mg/L.

Warning Signs of Nitrite Poisoning

These fish are known to show visible signs when they are exposed to higher nitrite concentrations.

• Rapid gill movement
• Gasping at the surface
• Staying near air stones or filter outlets
• Low activity or weakness
• Loss of appetite
• Poor balance or unusual swimming
• Dark or brown-looking gills
• Sudden unexplained deaths

The gills’ brown coloration will only become visible when the disease is quite advanced. Monitoring the water and observing fish behaviors are often better ways of diagnosing the problem than looking out for gills’ color.

If the fish continue to gasp even after the nitrite concentration has dropped, then you should look into the ammonia levels, water temperature, oxygen content, chlorine poisoning, and potential gill disease problems.

Lowering Nitrite and Nitrate Together

The first thing one should learn to reduce nitrates and nitrites in a fish tank is that they are related but need different ways to solve the problem.

Partial water change reduces both compounds instantly. After partial water change:

• Nitrite is regulated by a well-developed biological filtration system.
• Nitrate reduction is done by regular partial water changes, controlled feeding, stocking properly, waste removal, and growing plants.

Living plants can help in managing the nitrogen cycle in the aquarium in the long run; however, they should not be considered as a solution to a critical increase in the level of nitrite.

When the concentration of nitrate increases and ammonia and nitrite levels are zero, the biological filter works fine. Thus, the aquarium needs nitrate management more.

Preventing Another Nitrite Spike

Maintenance on a regular basis is the best way to keep nitrite out of your aquarium.

• Add new fish slowly.
• Don’t overcrowd the aquarium.
• Do not feed too much; only what the fish can consume.
• Remove any dead organisms and decomposed plants.
• Ensure that the filter is always operating.
• Ensure that the biofilter media is maintained.
• Clean different sections of the aquarium on different days.
• Condition new water from the tap.
• Maintain a good level of oxygen and water circulation.
• Monitor pH and alkalinity levels whenever there is instability in the cycle.
• Test for nitrite after medication, loss of power, filter change, or addition of new fish.

The best way to reduce nitrites in an aquarium is not relying on one container. Long-term control of nitrites is through clean water, reduction of waste, proper oxygenation, and biological filtration.