Skip to Content

Why You Have A Nitrite Spike After A Water Change!

After we published our article going over issues in an aquarium where you have no ammonia but high nitrite levels, we noticed a number of people reaching out to ask about having a nitrate spike after a water change in their aquarium.

Due to the majority of people doing a water change to intentionally reduce the amount of nitrites in their aquarium water, it is only natural to reach out for advice if you actually see the opposite being true in your aquarium.

Thankfully, provided you stick to a regular water change schedule, this should all balance itself out but we still wanted to publish a dedicated article on the topic to try and help as many of our readers having issues with nitrite spikes in their tank after a water change as possible.

One thing that we do want to say before we go any further is that you should not instantly do another partial water change after noticing that your nitrites have spiked after a water change.

This does seem to be a common thing that we see people trying but it should be avoided and we will explain why below…

Is It Normal For Nitrite Levels To Spike After A Water Change?

It is not normal for nitrite levels in an aquarium to spike after a water change but there are some very specific situations where this may happen.

It is not usually due to an error that you have made and is just one of those quirks of fish keeping where in some situations, things just don’t go to plan.

Why Did My Nitrite Spike After Water Change?

There are three main reasons that the nitrite levels in your tank can spike directly after a water change.

The first is due to the new water killing the bacteria that breaks nitrites down, the second is due to the natural nitrite cycle landing at the same time as a water change making them spike, and the third is due to a faulty water test kit.

New Water Killing Nitrite Eating Bacteria

The most common reason that you will see a spike in nitrite levels after a water change is due to the new water killing the nitrite eating bacteria in your aquarium.

Unfortinatley, this is just one of those things that naturally cycle in your tank depending on the exact parameters and condition of the tanks internal eco system.

The bacteria that eats nitrites in your tank can sometimes be at low levels in your tank and all water changes will unfortunately kill some of this bacteria.

If the water change lands at the same time as the beneficial, nitrite eating bacteria being at a low in your tank then the nitrite levels can spike.

This is totally natural and usually nothing to worry about and it should be cleared up and normalized by your next water change.

Some people will correct this by supplementing the water of their aquarium with high nitrite levels with the water from another aquarium to balance things out but this is usually not required in most setups.

The Nitrite Cycle

Another less common reason that nitrites can spike after a water change is due to the nitrite cycle itself.

The nitrite cycle is essentially the process that takes place in your aquarium when your beneficial nitrifying bacteria are growing and maturing to the point where they can efficiently break down ammonia in your tank into nitrites and then break down the nitrites into nitrates.

Ammonia -> Nitrites -> Nitrates

By total chance, you may do a water change in your aquarium where the nitrifying bacteria in your tank is working on breaking down a large batch of ammonia that then results in a spike in your nitrite levels.

This is essentially the previous step in the full cycle that we covered in the previous sections but this is totally normal and natural and usually nothing to worry about.

Just like the new water harming the nitrifying bacteria in your tank so it can’t break down the nitrite, this issue is based around that exact same bacteria.

This time though, you are just doing a water change at the same time of the cycle where your nitrite levels will spike even without a water change.

A Faulty Test Kit

The final common reason that nitrite levels spike after a water change is due to a faulty nitrite test kit.

This is not as common as the other two issues but it can still occur from time to time and is always worth considering if your nitrites are spiking for no obvious or apparent reason.

A cheap water test kit, especially the low quality strips will commonly give inaccurate readings and cause a number of problems within the fish keeping hobby.

This is technically not due to a nitrite spike in your water but your faulty test kit incorrectly reporting a nitrite spike in your tank.

Although these cheaper test kits are very inaccurate, simply retesting your aquarium water multiple times with fresh test strips can give you the true nitrite reading in your tank. Ideally though, you should be upgrading to a better aquarium water test kit if possible to avoid this problem in the future.

How Long Does A Nitrite Spike Last?

Nitrite spikes can last for a number of days or even weeks in your aquarium and it really depends on the nitrifying bacteria levels in your tank as to how long it will take for the nitrites to be broken down into nitrates.

As we covered in the previous sections, nitrites are broken down by nitrifying bacteria in your aquarium and this is the same nitrifying bacteria that can be harmed by new water changes in your aquarium.

This means that if you do a water change and it harms the nitrifying bacteria in your tank, it will also take longer for this nitrifying bacteria to recover and start breaking down the nitrites in your tank.

In a mature and established aquarium, nitrites should be broken down relatively quickly as there will be a large number of nitrifying bacteria present in the aquarium to break it down efficiently.

How Do You Fix Nitrite Spikes In Your Tank?

The best way to fix a nitrite spike in your aquarium is usually to just do a partial water change of between 20% and 30% of total water volume. Unfortinaltey, if you are seeing a nitrite spike in your tank after a partial water change we would recommend that you just wait for around a week.

This is usually enough time in most aquariums for the nitrifying bacteria to build back up in their cycle and allow you to do a water change with minimal issues with your nitrite levels spiking up again.

We know that there are some chemical products on the market that you can try to use in your tank and if you really want to get them then you can. For most people though, just waiting another seven to ten days before trying another partial water change will probably be the best option.