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High Nitrites and Nitrates During Cycle

High Nitrites and Nitrates During Cycle

The nitrogen cycle may be referred to as the new tank syndrome or biological cycle. However you may call it, it is necessary when setting up a new tank. The nitrogen cycle will help establish safe conditions in your tank for your fish to live in. It will help break down the food and waste in the tank and convert it into a nontoxic nitrate in your tank. 

High nitrites are caused when bacteria convert ammonia or fish waste into nitrites. The high nitrites are necessary to establish nitrate bacteria to grow and complete your cycle. If your nitrites become too high they can cause the cycling of your tank to stall. 

Below, we learn about the nitrogen cycle, what causes high nitrites, how to treat the high nitrates, and how to complete the nitrogen cycling process. 

What is the Nitrogen Cycle? 

Fish are living creatures that produce waste. These waste products are broken down into ammonia which can be harmful to fish. In an enclosed fish tank, it can reach toxic levels in a matter of a few hours. The nitrogen cycle will help avoid a dangerous environment for your fish. It will encourage the growth of beneficial bacteria that will help break down the waste from your fish. 

The nitrogen cycle will encourage bacteria to become established in your tank and filter media to convert the ammonia into nitrite and then nitrates which are safe for your fish. High nitrate levels can be toxic to fish and cause algae to bloom in your tank. If you’re experiencing algae blooms you will need to perform water changes to bring the levels back to normal.   

Nitrogen Cycling with Fish Or Without

It is recommended that nitrogen cycling be done before adding fish. There will be high levels of ammonia and nitrite in your tank which will not be an optimal environment for your fish. When the cycling process is completed it will be able to break down and convert the fish’s waste into harmless nitrogen. 

Cycling with fish is possible and may even be necessary if the tank has not been cycled or the beneficial bacteria has been lost. Cycling with fish may cause them harm or be fatal to your fish. Some fish are more tolerant of the cycling process, but it should only be done when necessary.   

Will High Nitrites Stall the Nitrogen Cycle?

When you are cycling your tank, the ammonia levels will rise before plummeting when the nitrite bacteria are formed. The nitrite levels will continue to increase until the nitrate bacteria can form. If the nitrite levels become too high they can inhibit the bacteria growth and stall the cycle. This is common if the process is rushed or there is too much ammonia added too quickly. 

When the nitrites become too high, it will be necessary to do water changes to continue the cycling process. The higher the levels of the nitrites, the more percentage of water you will need to remove for the water changes. You may be required to do multiple water changes to encourage the nitrate bacteria to form and for your tank to be fully cycled. 

How Long Should Nitrite Spike When Cycling Tank?

The length of time your nitrite levels will spike will depend on your tank, temperature, and pH levels. It can take anywhere between 2-6 weeks to complete the cycling process. Nitrite levels will rise at the end of the first week. They can remain at the same level for a few weeks or longer and when they begin to drop it can be a rapid process, even occurring overnight. 

The nitrite spike may continue for 2-4 weeks during the nitrogen cycle. The ammonia levels should remain between 2-4 ppm and should be tested every day. Re-dose with ammonia to 4 ppm when needed. If your nitrite levels are too high or do not begin to drop, your cycle may have stalled. Water changes are the only way to reduce the nitrite levels and continue the cycling process. 

Why Are My Nitrites So High?

Nitrites rise when the bacteria form and begin converting the ammonia into nitrites. Nitrite is required to form the beneficial nitrate bacteria. The nitrites will increase when too much ammonia is added too quickly to the cycling process. High nitrate levels can stall the cycling process. The nitrate bacteria will not grow at high nitrite levels. The only way to reduce nitrate levels is by water changes. 

Care must be used when cycling with your fish as it is stressful for your fish. Adding aquarium salt to freshwater tanks will also help keep nitrate levels down. This will be less stressful on the fish and live plants as well as the bacteria you are attempting to grow. Nitrite levels should be kept below 5 ppm. Any nitrite levels over 20 ppm can be fatal for your fish. 

How High do Nitrates Get During Cycle?

When your nitrates begin to rise and the ammonia levels are zero, your tank is cycled and ready for fish. Low-level nitrates are not toxic to fish. Some aquariums are kept at 5 to 10 ppm. Levels over 20 ppm are toxic to fish and need to be reduced. Regular water changes will be needed to maintain the proper nitrate levels in your tank. 

Removing fish waste when cleaning and adding aquarium plants to your tank will help maintain nitrate levels after the cycling process is completed in freshwater tanks. In saltwater tanks, live rock and sand beds will have areas where bacteria can break down nitrates into harmless nitrogen gas, and keep your tank at the optimal levels for your fish.   


High nitrate levels are necessary during the cycling process to encourage the growth of nitrate bacteria. The high nitrate levels can be caused by adding too much ammonia and stall the cycling process. Water changes will be necessary to reduce the nitrate levels to produce the nitrate bacteria. 

When your tank is showing nitrate levels and no ammonia, your tank is fully cycled and ready for fish to be added.  

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