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Why Do I Have No Ammonia But High Nitrite In My Aquarium?

Managing an aquarium properly to keep the water quality high and all the fish healthy at all times can be a major challenge, and if your aquarium has high nitrite but no ammonia, you might be feeling really puzzled and frustrated.

Usually, ammonia causes nitrite, and therefore bringing down the ammonia levels will bring down the nitrite levels, but you do need the right bacteria to deal with the nitrite. High nitrite levels can be challenging to handle, but it’s important to do so for the sake of your fish.

Nitrite is a really problematic thing to have in an aquarium, and it is caused by the ammonia that comes from fish waste and decaying food in the tank. You don’t want any nitrite in your active tank – at all, under any circumstances.

If you take a water reading, it should show zero parts per million (ppm) as this is the best situation for your fish.

Usually, if you minimize the ammonia in the tank and there are some bacteria to feed on the nitrite as it is produced, your reading should be extremely low or at zero.

However, there are situations in which the nitrites can get out of hand, even if the ammonia levels are low. It’s important to recognize this and understand how to address it for the sake of your fish.

Can You Have Nitrite Without Ammonia?

The only time you are likely to encounter nitrite without ammonia is when you are setting up a new tank and the bacteria that process nitrite have not yet got established.

It’s possible to have nitrite without ammonia, but this is quite a rare situation and you will probably not encounter it at any other time.

The only other instance in which it may appear is if you have had an ammonia spike that has been dealt with, and now the nitrite spike is following; this often takes a few days or weeks to occur.

When you first set up a tank, before adding fish, you will need to cycle it to ensure that you create a balanced system that the fish can survive in. There will not be enough good bacteria in water that has come straight from your taps, and if you fill a tank with this and then add fish immediately, they will probably all die very quickly.

To cycle a tank, you need to add ammonia to it, and then keep doing partial water changes while the tank balances and the different kinds of bacteria establish a foothold within the system.

It is perfectly possible to have readings that show high levels of nitrite but absolutely no ammonia during this cycling period, even if you are regularly adding ammonia to it to help it balance.

The ammonia levels may keep going down, while the nitrite levels may not seem to change at all.

Why Do I Have No Ammonia But High Nitrite?

If you are adding ammonia to the water and then taking regular readings, you may find that the nitrite level remains high and the ammonia level keeps going down; this is fairly normal.

It can be explained by the fact that the bacteria that feed on ammonia tend to grow and get established more quickly than those that feed on nitrite, and therefore they will more quickly process the ammonia in the tank.

You will have to wait quite some time for the nitrite bacteria to get established enough to deal with the nitrite in the tank, particularly if this level is high.

Once the bacteria that process nitrite have got established, you should start to see the levels dwindling, but it is important to be patient, as this could take a few weeks.

There are many different theories about how to speed the process along, but often, simply being patient and doing partial water changes will be sufficient – although you may need to be very patient, especially if you have high levels of nitrite.

Don’t be discouraged if your readings show high nitrite and no ammonia day after day, even if you are adding ammonia.

It really isn’t uncommon for the nitrite level to spike during the early weeks, before the bacteria have managed to get established, and once the levels of bacteria finally get high enough, they will deal with the nitrite. 

How Do I Lower Nitrites In My Aquarium?

You can purchase bottles of bacteria for your aquarium, but these will usually do very little when you are cycling the tank, and they can be an unreliable solution because they often die during storage and transportation, and you won’t have any way of knowing whether they are still active or not when you add them to your tank.

The most effective way to lower the nitrite level is to perform regular partial water changes with dechlorinated water. However, this can be stressful for the fish if you already have the tank stocked, so do so with care.

Often, you will be changing around thirty percent of the water per day, preferably split into two changes of fifteen percent each, with around two hours between the changes.

Be aware that your nitrite levels should never be higher than 0.25 in any tank, and this is still considered a somewhat dangerous level. 

Keep testing your water and completing thirty percent changes until you have started to bring the nitrite levels down, or you are at great risk of losing your fish.

Remove any waste or leftover food that you can and ensure the tank is clean, as nitrite is produced by waste, so cleanliness should help to stop the levels from climbing.


An aquarium with high nitrite and no ammonia is an unusual thing, but it certainly does happen, especially when you are cycling a tank and getting it established in preparation for adding fish. Keep persisting with water changes and allow the bacteria that process nitrite to catch up; this may take some time, but they will get there. Patience is key in dealing with this issue, and only once the tank has balanced should you consider adding fish.