How to Lower Nitrates in Aquarium (Reduce Them For Good)

how to lower nitrates in aquarium
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Last Updated: July 11, 2022 by Flora Gibbins

In and of themselves, elevated nitrate levels aren’t especially deadly to fish and most other aquarium creatures.

But then…

The problem with high nitrate levels is these molecules are the last step in the aquarium nitrogen cycle that converts ammonia to nitrite, and then nitrate.

Once nitrate is produced, there are no other micro-organisms in the tank that can break it down.

Learning how to lower nitrates in an aquarium is important because high nitrate levels can lead to deadly algae blooms.

Overview

In nature, fish, aquatic plants, and other living things have lived together successfully for millions of years.

They do so because each organism consumes something and produces waste. That waste, in turn, offers some kind of benefit for another creature in the ecosystem.

Once you duplicate this natural rhythm and balance of life in your aquarium, there is little, if any need to be concerned about mechanically reducing nitrate levels in your aquarium.

Ammonia, Nitrites, and Nitrate Levels Within the Nitrogen Cycle

To mimic nature’s way of dealing with increasing nitrate levels, you need to where they come from and why.

Once you know how it works in nature, it is very easy to figure out how to reduce nitrates in aquarium.

Elevated nitrate levels are the end result of a series of processes that begin with aquatic animals. Fish, shrimp, snails, and other creatures in the animal kingdom excrete waste. This waste is either directly in the form of ammonia, or converts to it.

Uneaten food, dead leaves from plants, and other organic material also break down into ammonia in an aquatic habitat.

Ammonia, in turn, is very deadly to fish and other aquatic creatures. Fortunately, some bacteria consume ammonia and convert it to nitrites.

A high nitrite level is also dangerous to fish and other aquatic creatures, but it takes a higher concentration than ammonia.

From there, another species of bacteria breaks the nitrites down into nitrates.

The beneficial bacteria that break down ammonia and nitrites take time to establish in new aquariums and those that have been treated with antibiotics.

This is why you should never put fish into a tank that hasn’t been “cycled”, or have gone through at least one surge of ammonia and nitrates. Once the tank water is at zero for both chemicals, it is ready for fish and other creatures.

Live Aquarium Plants and Maintenance

As in nature, there are no bacteria that break nitrates down into something less toxic. Instead, plants pick up where bacteria left off.

As with land-based plants, aquatic plants use nitrogen as a source of food.

aquarium with fish and aquatic plants

Therefore, when you put live plants in a freshwater or saltwater aquarium, they effectively complete the nitrogen cycle and also reduce nitrate levels.

Most advanced aquarium keepers arrive at plants as the best answer to the question “How to reduce nitrates in aquarium?”

From there…

You have two options for maintaining the plants:

  • Add a few fish or other aquatic creatures that snack on plants to the tank. Just make sure the plants can grow fast enough to keep up with the fish.

I’ve used fish to control plant growth in larger tanks, however, found trimming worked better in tanks that hold less than 20 gallons.

  • Simply trim the plants on a bi-weekly or monthly basis so that the leaves don’t die off and rot back into ammonia. This is an essential step in learning how to lower nitrate levels in aquarium.

Regardless of the method you use, there is a difference between spurring plant growth with pruning and preventing the plant from making new growth.

Every species of plant is a little bit different, as is every aquarium setup. I recommend starting with slow pruning or just one fish, and then see how each plant responds.

When using live aquarium plants for controlling nitrate levels, you must always be aware these plants will also compete with algae.

If there is a tendency towards a high nitrate level and a lot of light, algae can and will suffocate plant leaves and deprive them of light.

In these situations, I recommend careful, temporary usage of fast-growing surface plants to absorb the nitrates as quickly as possible.

If you do use an extremely rapid-growing surface plant, you still need to be careful about oxygen levels in the tank and any loss of surface tension breakage that might occur.

Controlling Excess Food and Fish Waste

When you feed fish, there should be no food left after 5 minutes. If you see food sitting at the bottom of the fish tank after this time, it is a problem you need to solve.

man hand feeding aquarium fishes

Learning how to lower nitrate levels in aquarium via food management is something that requires observation first.

Simply adding less food may not be the answer, especially if you notice that some fish in the tank aren’t eating at all.

Here are some things you should do before simply cutting back the food amount:

Make Sure you Know Which Tank Zone the Fish Prefer

Different species of fish will choose the upper, mid, or lower levels of the tank as the primary site for consuming food.

For example, bettas will rarely eat at the bottom or mid-levels of the tank even if the food is sitting there.

Tiger Barbs will rush to the top, but then they will drop to the bottom of the fish tank to scavenge. Angelfish and tetras will capture food at the top of the tank, mid, and then scavenge at the bottom.

Fantails will go up to the top of the tank, but they tend to have fewer swim bladder problems if they stay in the lower part of the tank. Similarly, bottom feeders won’t even come to the surface or mid-level to eat.

The best way to manage this is to choose different food forms so that the particles go where the fish will eat them quickly.

When answering the question “How to lower nitrate levels in a freshwater aquarium?”, start off with food forms for bottom feeders. In this case, use sinking pellets if you have these kinds of creatures in the fish tank.

Use micro-pellets or other floating food in combination with this if you also have fish in the tank that prefer to eat at the surface or mid-levels.

When you divide the food by form, do not increase the amount of food in the tank. Instead, adjust the ratio of each food type to match the needs of the fish in the tank.

For example, if ¾ of the fish in the tank are upper and mid-level eaters, then ¾ of the food would be micro-pellets or flakes. The remaining ¼ would be sinking pellets for the bottom feeders.

Make Sure the Fish are Comfortable Eating the Food Form

There is no question that freshwater aquarium keeping can be an expensive hobby. Sadly, many beginning and even advanced aquarium keepers try to cut corners when it comes to food options.

This usually means people will buy flake-based foods because they are the cheapest. They are also the most deadly thing you can give fish for several reasons:

  • Flake-based foods are usually made with lower quality ingredients. This means even “color enhancing” formulas won’t have the best ingredients to support internal health.
  • Flake-based foods can easily choke your fish. These foods tend to soak in aquarium water and swell very quickly. If the flakes are moist enough, they can stick to the fish’s throat and create a clog.
  • Fish don’t like to eat them and will leave them to rot. To add insult to injury.
Flake-based foods foul the water faster because they break down faster than other food types.

fish eating food flakes

This is why when applying an answer to “How to remove nitrates from fish tank?”, avoiding flake foods is very important.

Even though pellet-based foods aren’t always the best option, they are better for staple or routine feeding. They don’t take on water as quickly, and won’t choke the fish.

Overall, live food is always the best for fish, since it mimics what the fish would eat in nature. If this isn’t possible, frozen foods are a good option.

I tend not to like freeze-dried foods because the fish can choke on them, or simply avoid them at all costs.

Here again, aquarium water fouling is an enormous problem. It is also why avoiding certain freeze-dried foods is an appropriate answer to the question “How to lower nitrates in fish tank?”.

Manage Your Own Food Distribution Habits

If you are a novice to aquarium keeping, there is a tendency to overfeed the fish. I found the best way to solve this is to divide a daily ration in half.

This isn’t always helpful when fish figure out that coming up and wiggling their fins at you will result in more food.

Make no mistake, aquarium fish absolutely study the outside world and make plans to get what they want.

I have seen everything from bettas to cichlids use eye contact, fin motions, and anything else that they conclude will pry a snack out of me.

As a result, I believe firmly in setting aside little tidbits like live brine shrimp, so if the fish are begging, I have something to give them.

Since brine shrimp are very small, releasing a dozen or so into the tank won’t create much of a bioload. In addition, if you have fish in the tank that tend to be carnivores, they will enjoy hunting the brine shrimp.

Every now and then, you may have a single fish in a hospital, quarantine, or other special situation tanks. If the tank holds more than 5 gallons, you can go ahead and add thawed blood worms, daphnia, or anything else the fish might enjoy.

For vegan fish or others that primarily consume plant-based material, I just make sure I have plants in the tank that grow fast enough to keep up with their snacking.

In this way, fish get their extra snack, plus increased plant growth provides a natural answer to the question “How to remove nitrates from aquarium water?”

Fun Fact: You can learn more about proper aquarium tank cleaning and maintenance by reading our post on How To Clean A Betta Fish Tank (Correctly). The tips, hints, and insights presented are applicable to all types of fish tanks regardless of your pet fish species!

Ammonia Lock Ups and Their Impact on Nitrates

Over the years, I’ve taken part in some stiff debates about what to do if a tank suddenly shows signs of an ammonia surge.

Far too many people say “do a 50 – 100% water change”. And this is why far too many people wind up with a tank of dead fish.

While they are focusing exclusively on the ammonia, they are losing track of the pH, hardness, and anaerobic bacteria floating in the tank.

In the process of solving this one problem, they are creating others just as deadly to the fish. Even though it may take a few days to a week for the diseases or sudden fish deaths to occur, rest assured the aquarium water chemistry fluctuations are the cause.

The bottom line is fish and other aquatic creatures are already stressed out from living in confinement.

Just because a species can take a “wide range” of water chemistry parameters, that doesn’t mean they can handle large fluctuations like you get with massive water changes.

Unlike in an aquarium, the water chemistry parameters in a pond or stream change gradually. Even captive-bred fish are just not designed for large water chemistry swings.

This is why I recommend keeping zeolites and other ammo lock-up material in the filter at all times. They can help head off an ammonia surge.

The problem with zeolites and other ammonia lock-up products is they rapidly convert ammonia into nitrites. This means if you have too much zeolite in the tank, then you may limit the bacteria population that consumes ammonia.

As you can see in this video, aquarium keepers of all ages have different views on this topic.

I still find these products very useful, especially in the first year of a tank operation. They provide an excellent backup while figuring out the feeding dynamics in the tank.

Nitrite and Nitrate Levels Reducing Pads

During the first year to a year and a half, most aquariums will need some form of chemical assistance, or a nitrate remover when it comes to ammonia and nitrite management.

Within that context, the answer to the question “How to fix nitrate levels in fish tank?” will change as the tank water and its inhabitants age.

Here are factors that you may not be thinking about that can still generate sudden surges during this time:

  • Most tropical fish will double or triple in size during the first year in a home tank. This means double to triple the amount of waste and food consumed in a very short time.
  • Younger fish in a strange setting tend to become stressed more easily. As a result, they will emit more ammonia from their gills.
After the first year and a half, I recommend keeping nitrite and nitrate-reducing pads or chemicals on hand.

They will come in handy if you decide to add more fish, plants slow down in growth, or something else happens.

Just be careful about the types you choose, since some may not actually work.

Fun Fact: Carbon filters provide better nitrate control compared to sponge filters. However, you have to maintain the former regularly to keep it operating to its full potential! Get answers on how long does carbon last in an aquarium filter to prevent nitrates from poisoning your pet fish.

Frequently Asked Questions

Are some aquatic creatures more susceptible to nitrates than others?

Freshwater shrimp may be a bit more susceptible to nitrates. Most fish and other creatures won’t have a problem.

It is still important to learn how to get rid of nitrates in fish tank if you want to take care of more delicate creatures or saltwater tanks.

What is the biggest danger if nitrates go too high in my aquarium?

The biggest danger is it will feed an algae bloom that will die off and produce ammonia once the nitrates are gone.

Should I respond to a high nitrate level with extreme reduction measures?

I don’t believe so because you can use plants and nitrate-absorbing plants to solve the problem. Water changes using bottled or tap water, and other rapid responses do more harm than good.

Conclusion

You may be very concerned when you see the nitrate level rising in your home aquarium. It is best to take measured actions that balance the tank naturally as opposed to doing a water change.

When you use methods that mimic nature in your home tank, the inhabitants of the tank will be more comfortable, and you will enjoy not having to manage one emergency after another because of lethal water change-related chemistry disruptions.

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