How To Lower Nitrates In Fish Tank

Maintaining a healthy fish tank is as important as anything if you have an aquarium. When you neglect regular maintenance, get ready for some unusual happenings in your tank and to your fish.

One of the common problems long-term aquarists face, and you’re likely to face if you’re a newbie, is a nitrate spike in your fish tank. This could mean nothing or many things, depending on the kind of tank and fish you keep.

If it’s a big problem, you need to learn how to lower the nitrate concentration in your fish tanks. Moreover, why does nitrate matter in fish tanks, what are the implications, and how can you deal with it?

You’ll find answers as you read through.

Appropriate Nitrate Level in Freshwater and Saltwater Fish Tank

Nitrate is usually at the normal level in fish’s natural habitat, and there’s hardly any active maintenance done; it is usually below 5 ppm. However, in a controlled habitat like a fish aquarium, nitrate levels rise quickly and are sometimes beyond control.

Generally, spikes in nitrate levels don’t really matter in a freshwater tank and may not affect the fish much. But, it’s better to keep nitrate at safe levels, like between 25 to 50 ppm. 

If you have fry in your freshwater tank, then the ideal level shouldn’t be less than 10 ppm. On the other hand, saltwater fish tanks cannot handle excess nitrate.

It can be very bad for your invertebrate and coral. Here, the nitrate level should always be below 5 ppm. If you keep marine fish, they can still function well at 40 ppm nitrate levels.

Excess nitrate can be problematic and requires swift response to protect fish health. But before getting into how to lower nitrates in fish tanks, you need to know things responsible for excess nitrates so you can avoid them next time.

What Causes Excess Nitrate?

How To Lower Nitrates In Fish Tank

General lack of aquarium maintenance and other factors are causes of excess nitrate in fish tanks. Nitrate is the end product of bacterial reduction of ammonia, which turns to nitrite, then eventually, nitrates.

In addition, they can stay in your tank for a long period until you do something about it. What are the possible causes of excess nitrate?

1. Overstocking aquarium

Overstocking your aquarium with too many fish can cause nitrate spikes in your tank. Having numerous fishes can result in excess fish waste, making nitrate rise to an unbearably high level. Try getting a new tank and cutting down on the ratio of the fish to the tank.

2. Decaying plant materials

Leaving decaying plant materials in your tank can make bacteria in your aquarium convert to ammonia, then nitrate. This is majorly due to negligence of the tank’s maintenance. Therefore, watch your aquatic plants to remove decaying ones.

3. Dirty filters

Keeping dirty filters in your aquarium can cause excess nitrate in your fish tank. For example, the dirt will prevent beneficial bacteria from removing nitrate.

4. Detritus

Accumulated dead organisms and fish waste, detritus, at the bottom of your fish tank can increase nitrates and give room to more harmful organisms in your aquarium, like algae.

5. Water source

Sometimes, even when you have a clean tank and do a routine water change, you’ll still notice excess nitrate in the aquarium. This is mostly due to the water source, moreover, the water you pump in your tank could be the problem.

6. Lack of live plants

When there are no live plants in your tank, you can expect the nitrate levels to be high. Generally, live plants can help improve your aquarium’s overall health.

7. Overfeeding fish

Overfeeding fish is one of the major causes of raised nitrate levels in fish tanks. Your fish let out too much waste in the tank when you do. Fish waste and excess food rot in the tank increase nitrate.

8. Poor tank maintenance

Not maintaining a clean tank and neglecting routine checks can make nitrate increase.

Implications of Excess Nitrate in Water

Generally, excess nitrate can be bad for your fish and lead to worse situations or deteriorating fish health. Some implications include:

1. Nitrate poisoning

An extreme level of nitrate toxicity is nitrate poisoning. When the nitrate levels remain high for weeks, your fish will experience nitrate poisoning. Eventually, your fish fall sick, and if you don’t do something about it, it could cause your fish to die.

2. Nitrate shock

Sudden exposure to high nitrate levels can cause nitrate shock, making your fish vulnerable to death in 24 hours. It often happens when you introduce your fish to a tank with a high nitrate concentration or carry out sudden water changes.

3. Decreases oxygen level

Excess nitrate in fish tanks can cause a decreased oxygen level, affecting your fish, live plants, and other living aquatic animals in your aquarium.

4. Stressed fish

Consequently, excess nitrate will stress your fish, and you’ll notice it in the way they behave in the tank.

5. Algae growth

Excess nitrate levels will eventually cause algae growth and bloom in your tank, which is another thing you don’t want to deal with.

Symptoms of Nitrate Poisoning in Fish

Symptoms of Nitrate Poisoning in Fish

Fish can show different symptoms of nitrate poisoning that you probably were not paying attention to. When you notice strange behaviors in your fish, you should always check.

Anyway, the symptoms of nitrate poisoning in fish are:

  1. Lethargy or fish laying on the tank’s substrate.
  2. Increased breathing and gill movement.
  3. Poor appetite or lack of it.
  4. Disorientation and fish’s inability to swim properly.
  5. Fish curl from head to tail.

How To Test For Nitrate in Fish Tank

You need to test your aquarium monthly to check the nitrate levels. This should be part of your routine tank maintenance.

To test your fish tank for nitrate, you need a test kit which could either be liquid or paper strips. Many people prefer the liquid strip because they seem to be more accurate.

You only need to scoop some of the water and use the test tool to check the nitrate level. Apart from testing the tank, you also need to test your tap water to check the nitrate level.

How To Reduce Nitrate in Fish Tank

Every aquarist should know how to lower nitrates in fish tanks in case the situation arises. Doing that isn’t hard.

Here are the things you can do:

1. Maintain a clean tank

One of the ways to prevent and lower nitrates in fish tanks is by routinely cleaning and maintaining a clean tank. Remove excess fish waste and leftover food. In addition, you also need to remove decaying plants from your tank and ensure you maintain routine tank maintenance.

2. Keep live plants

You can also introduce new live plants into your fish tank and remove the rotten ones. Live plants use up nitrate in the tank as fertilizer and enable their growth. 

Not only will it lower the nitrate level, but it will also help to ensure that your tank maintains the ideal level for fish to stay healthy. 

Some plants to put in your tanks are:

3. Use a refugium

You can also install a refugium in your aquarium to protect your fish from high nitrate levels. It’s like an isolated place that can serve as a refuge for your fish. 

A refugium is also a place where you can cultivate macroalgae, which effectively lowers nitrate in fish tanks.

Check out some of these refugia:

4. Use filter media

When high nitrate levels remain persistent in your fish tank, it could be the water source. What you can do is use nitrate-removing filter media in your aquarium.

This will help reduce the amount of nitrate that gets into your fish tank.

You can get some nitrate-removing filter media online like:

5. Water change

You can also lower nitrates in your fish tank by changing the water in your aquarium. But first, you need to test the water you want to put in the aquarium. This test will be to confirm whether it is at the appropriate level to prevent your fish from shifting to nitrate shock from too little nitrate level.

6. Use microbes

Another thing you can do to lower the nitrate level in your aquarium is by introducing live microbes into your fish tank. Microbes use nitrogen as biomass or convert them into harmless nitrogen gas.

However, you should be careful with microbes, especially the aerobic ones, because they can multiply and cause oxygen depletion in your aquarium.

7. Use a denitrator filter

Denitrator filters are natural nitrate-removing filters you can use in your fish tank. When you use this, you don’t necessarily need to use a filter media; it’s either of them, and you can select the one that matches your budget.

In addition, the denitrator also removes nitrogen from your tank. 


High nitrate levels in your tank are bad for your fish, and you need to remove them as soon as you notice any strange behavior in your fish tank. Moreover, it is essential for you to know how to lower nitrate in fish tanks.

First, try water changes by testing the water prior, then try other solutions if the situation persists. Once you have your tank at the level you need, ensure you check nitrate every month and maintain your tank to prevent it from happening again.

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