How to Lower Nitrate Levels in Your Freshwater Fish Tank

How to Lower Nitrate Levels in Your Freshwater Fish Tank

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Although nitrates in aquariums are not as harmful to fish as ammonia or nitrites, a high nitrate concentration in your water column will result in several issues including algae overgrowth.

For that reason, you want to keep nitrates in check, preferably anywhere between 20 and 25ppm.

But exactly how do you reduce the concentration in case of a buildup in your tank?

Well, there is not a single silver bullet type solution, but a blend of these measures will most certainly remedy an excess nitrate situation, in any freshwater aquarium.

  • Regular water changes
  • Adding live plants, especially nutrient hogs like hornwort
  • Reducing fish populations in line with the recommended species stocking rules
  • Regulate feeding and cut back on the amounts you feed the fish if you have a lot of leftover after every feeding session
  • Cleaning your fish tank regularly, which includes washing your filter media and vacuuming your substrate
  • Using nitrate removers

Please read on for more insight on how to deal with nitrates in your freshwater aquarium, including a detailed look at all measure mentioned above.

What Should Nitrate Levels Be in Freshwater Tanks?

The recommended level of nitrates in freshwater aquariums is anywhere from 20ppm to 25ppm, although it’s more desirable to have a lower reading, maybe between 5 to 20ppm, for an agreeable buffer zone in case of a rapid buildup.

Moreover, while breeding your fish, battling an algae problem or with messy fish that create constant water quality issues, keep your nitrates levels below 10ppm.

Also, nitrates levels in nature remain pretty low, resting at 5ppm or below, so when looking for the closest reading to a natural environment and one that will best replicate the fishes’ wild ecosystem, 5 is the number.

Having said that, it is not uncommon for some aquarists to run their levels as high as 30,40, and even 50ppm, and may advise you as much. But this is a risk because even when the high nitrates concentration may not affect your aquarium inhabitants in the short term, there will be a gradual development of issues that will manifest eventually.

The main problems associated with prolonged exposure of your fish to high nitrates levels (above 25ppm) is nitrate poisoning. But the rapid onset of nitrate levels in a fish tank can lead to nitrates shock.

One other thing to know is you will need to read your tanks nitrate levels to determine how much to lower them. To do this, buy and follow the instruction on the test kit.

Essentially, by matching the color of the test with those on the included color chart, you will know how much nitrate is in your water.

How to Remove Nitrates from Your Fish Tank

We’ve already determined that you would need to put several measures in place to reduce or remove nitrates in your fish tank.

But how does either of these measures work exactly, Let’s find out!

#1 — Perfome Regular Water Changes

Performing regular water changes particularly with water that has little to no nitrates will lower the overall nitrate levels in your aquarium.

The water changes help expel the water with high dissolved nitrates as broken down by healthy bacteria from ammonia through nitrites into nitrates.

I recommend you do more water changes than normals depending on the levels in your fish tank. Preferably, use RO water instead of tap water more so if your local water is high in nitrates, which is a major source of nitrates in aquariums.

#2 — Add Live Aquarium Plants

Live aquarium plants, same as algae, use the nitrates and other mineral elements in the water for their development. The plants get the nitrates from the water through their roots and sometimes stems, depending on the type.

Plant species that feed on the water column are especially suited for the job, which includes most floating aquarium plants that are not anchored in a substrate.

That said, some plants consume more nutrients than other mostly premised on the rate of development. Species that have a growth rate that is borderline weed-like, for instance, hornwort will expel more nitrates from your tank and in a shorter time than slow-growing plant like anubias. Its also possible that tall background and mid-tank plants are bigger nitrate hogs than short foreground plants.

6 Best Aquarium Plants to Reduce Nitrates

As I’ve mentioned, different aquarium plants will consume varying amounts of nutrients, including nitrates. See the list below for the best aquarium plants to reduce nitrates.


Hornwort is a submerged, free-floating aquatic plant that is popular in the aquarium hobby, though it is considered an invasive species in some places. The species is often used as a floating decorative plant in freshwater (both coldwater and tropical) aquaria and is by far the plants at reducing nitrates in freshwater aquariums.

This plant has many small, spiky leaves that form a large surface area for nitrate absorption, plus hornwort grows quite fast meaning it takes up nitrates equally as fast.

In the fish tank, a hornwort plant is easy to start, either floating or substrate, giving you freedom when designing the look of your tank. It also has a high tolerance to various water conditions hence a good choice for beginners.


Anacharis is the only other plant that can consume almost as many nitrates in a water column as hornwort.

Same as hornwort, anacharis has small, spiky leaves that form a large surface area for the absorption of nitrates.

An anacharis plant appearance is also quite attractive with a long stem and the small green leaves covering the entire length. It may also develop short white roots that grow from the base of the stem.

In the aquarium trade, the anacharis plant is also called Brazilian waterweed and is sold as an ideal species for beginners as it is easy to grow and able to start either in gravel or floating in the water column.


Vallisneria has a few long bladed leaves, which have a smaller surface area for nitrates absorption compared to the small leaves on hornworts and anacharis. However, the plant will still consume a lot more nitrate than a majority of aquarium plant species.

When starting Vallisneria in a fish tank, there are only two requirements to consider. First off, you must feed it, and the second is to provide it with light.

This way, your val plant will grow exponentially and consume as many nitrates as you want it to. The plant also looks good and is undemanding, with the potential to easily transform an aquarium into a luscious jungle.

Amazon Frogbit

Amazon frogbit, also called Indian sponge plant, South America sponge plant or Amazon smooth frogbit is another perfect species to use when you need to reduce nitrates in your fish tank.

It is a floating aquatic species with leaves that lie flat with the water creating a considerable large surface area for the absorption of nitrates.

Amazon frogbit also grows quite fast, sometimes up to 20 inches across in the home aquarium, and can easily spread across the entire surface of a tank.

Like the first three plants, Amazon frogbit is easy to care for, but make sure that top of the plant is kept dry at all times because if the plant leaves stay wet for a length of time, it will start to rot.

Water Lettuce

Watter lettuce is a beautiful aquarium plant that is sometimes called water cabbage or Nile cabbage. Although it can be a little difficult to grow in a home aquarium, this plant is quite beautiful and will sort out your nitrate problem with zero issues.

A water lettuce plant grows much like a head of lettuce or cabbage and then blooms and opens up like a flower. It can reach up to 10 inches across with leaves but no stem, and their surface is covered in short, soft hairs, which help the plants to trap air, increasing its floating capability.


Cryptocoryne, commonly referred to as crypts, is a genus of aquatic plants as opposed to a single plant, with several species that are grown in aquariums.

The most popular of the species is Cryptocoryne wendtii, which is a grown plant suitable for small aquariums. However, crypts also come in other color forms such as olive, and reddish-brown.

For best results in your fish tank, use cryptocoryne as a solitary plant, though it not a must. The plant can still be grown with others, but it will develop taller and narrower.

Overall, crypts are easy to care for and can grow under low to moderate light. You will, however, need to fertilize your crypt plants because they require a lot of nutrients for the best outcome.

That said, please note I’ve only listed the best nitrate consuming plants, but these species are equally as good.

  • Marimo moss ball
  • Echinodorus bleheri
  • Duckweed
  • Sagittatia
  • Moneywort

#3 — Reduce Your Fish Population

When your aquarium is overstocked, the amount of ammonia that has to be converted to nitrates is large, meaning some of it will be left unfiltered.

The problem gets worse when you lack a reliable filtration system because apart from high nitrate levels, you will very likely experience an ammonia spike.

For that reason, a fish tank should have a gallon of water for every inch of fish you add in the tank and up to two gallons per fish when keeping species with a more than average bioload like goldfish or oscar fish.

It is also important to know that not all aquarium fish are the same shape, and the body size is not limited to the fish’ length only.

Therefore, stocking a 10 gallons fish tank with ten inches of slender shaped zebra danio is not the same as stocking it with full-bodied goldfish.

Larger bodies fish create far more waste and therefore require more water volume.

#4 — Regulate The Feeding Schedule

On top of fish waste, uneaten food also decompose and release ammonia into your fish tank, which is then converted to nitrates.

So, to keep your aquarium free of leftover, only offer your fish amount they can finish in the shortest period once placed in the water.

A good rule of thumb is to feed your fish an amount they can consume in three to five minutes. A three minutes meal-time is better if you feed your fish more than once, while a five minutes duration is best while feeding them once a day.

#5 — Clean Your Fish Tank Regularly

Cleaning your fish tank help expel any fish waste, leftover food, and plant debris from surfaces such as aquarium glass, substrate, decorations, and plants.

Whereas, regular water changes help expel excess nitrates from the water column, especially if you do not have enough plants or items like lava rocks in your tank.

I highly recommend doing a 10 percent water change once every week and cleaning your fish tank at least one time in a month to keep the nitrates in your tank in check.

Aquarium gravel, plants, and decorations notoriously host loads of solid waste, so make sure you get into every nook and crevices while you clean them. Use a toothbrush to scrub solid detritus and an algae remover to remove any plant-like debris from the surfaces.

#6 — Use Nitrate Removers

Nitrate removers are specially formulated remedies like Seachem Denitrate that are used to reduce concentrated nitrates in fish tanks, plus solve any other problem associated with excess nitrate levels like cloudy aquarium water.

Most manufacturers will have indicated the appropriate amounts to use, but most products are just placed directly into the water column and start showing results in 48 hours.

I recommend using Seachem products because they have been around since forever, meaning they are tested and proven. Most freshwater aquarium fishkeepers I know use Seachem products quite often.

API nitrate removers and water clarifiers are good quality as well and are also recommended.

Lastly, remember to get a nitrate test kit to help you gauge how effective the remedies you implement are and which one has the best results.

Eddie Waithaka

Resident Content Creator and Marketer at AquariaWise who talks about aquariums and fish and aquascapes a lot.

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