6 Ways To Lower Aquarium Nitrates (& Why They’re So High)

Last Updated on 2023-08-30

If the nitrates in your aquarium are too high, then for the health of your fish, you should do everything you can to lower them! Fortunately, not only will this article show you how to lower the nitrates in your aquarium, but you’ll also learn what causes high nitrates, what the nitrate levels should be, how to test for nitrates, and much more!

So keep reading to find out everything you need to know about lowering the nitrate levels in your tank.

What Are Nitrates?

Before anything, it’s important to know what nitrates actually are. Nitrate is produced by fish waste, rotting food, and decaying matter in the tank. At first, ammonia is in the tank, and as that gets broken down, it turns into nitrite, and then finally, that gets broken down into nitrates.

What Should Aquarium Nitrates Be?

It’s best for the nitrates in your tank to always be below 20ppm; however, they can still be a little bit higher before they start damaging your fish. In fact, anything up to 40ppm can be safe. 

What Causes High Nitrates In An Aquarium?

If you have high nitrates in your aquarium, there are actually a few different things that may be causing it. So if any of the following is occurring in your tank, they will be behind it.


One of the most common reasons that the nitrates in your tank may have become so high is overfeeding. But not the overfeeding itself but rather the leftover food beginning to rot in the tank.


Aside from overfeeding, another extremely common reason that nitrates in the aquarium may be so high is that you’re overstocking the tank. If the tank isn’t big enough and you have too many fish, then the beneficial bacteria that eat waste won’t be able to get rid of it fast enough. 

Too Much Plant Waste

While plants are great for reducing the amount of nitrates in your tank, if you don’t remove old decaying leaves etc., then the amount of nitrates in the tank will go up over time, and they may even spike quickly.

The Filter Isn’t Performing Well Enough

And lastly, if your filter isn’t performing well enough, it could also cause a buildup of nitrates in the water. In some cases, the filter itself might not be powerful enough to keep up with the waste in the water, but more likely, you may simply need to change the filter media out if it’s been getting old.

Why Are High Nitrate Levels Bad?

There are a number of reasons you’ll want to keep the nitrate levels in your tank below 20ppm. In fact, if you don’t, it can have terrible consequences for your fish!

If the nitrate level in your aquarium is too high, then the following may happen:

Nitrate Poisoning

First of all, in severe cases, nitrate poisoning or nitrate shock may occur, which can end up killing the fish in your tank. While this isn’t as common as the other problems, it’s definitely still possible.

Shortened Lifespan

Even if nitrate poisoning doesn’t kill your fish, high levels of nitrate in the water are definitely going to reduce the lifespan of any fish in your tank. 

Increase Stress

High nitrate levels will also increase the amount of stress that fish feel. When the fish are stressed, it will make them more susceptible to disease and illness.

Stunted Growth

If you have fry or juvenile fish in your tank, then high nitrate levels may also be responsible for their stunted growth.

Poor Color

Because of the stress caused by high nitrate levels, you can also expect the color of your fish to be a lot more dull and boring. However, if you manage to keep the nitrate levels low, the good news is your fish should return back to their healthy, happy color.

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How To Lower Aquarium Nitrates

Now that you know what causes high nitrates in your aquarium and what the effects of high nitrates in your aquarium are, the next step is making sure you lower them down to a more suitable level!

Fortunately, there are plenty of ways you can do this, and they’re all incredibly simple!

Perform A Water Change

The easiest thing you can do to lower the nitrates in your aquarium is to simply perform a water change. By removing 20% of the water, not only will you remove 20% of nitrate, but you’ll further dilute the remaining nitrates in the tank with the fresh water. 

Add Live Plants

If you don’t have live plants in your tank yet, now could be the perfect time to get some! Live plants are a natural filter not just for nitrate but for nitrites and ammonia as well. On top of this, they’re also going to keep your tank well-oxygenated too!

Just remember to remove any leaf litter from your tank to maximize the reduction in nitrates!

Nitrate Removers

If you need to remove nitrates fast and you can’t perform a water change, then one of the best choices is chemical nitrate removers. If you’re not sure which nitrate remover to choose, then I’d recommend Seachem Denitrate.

Feed Your Fish Less

Another incredibly easy way to help reduce the amount of nitrite in your tank is to simply feed your fish less. If you’re feeding your fish, but they’re not eating it all, then the waste food will produce nitrates.

So start feeding your fish less, and if you notice any waste food in the tank a couple of hours after feeding them, then you should remove it as well.

Get A Bigger Tank

Sometimes, it may just be the case that the tank you have your fish in just isn’t big enough. No matter how good your filter is or how much waste you try to remove, if you have a tank that is overstocked, then the nitrate buildup will always be out of control.

Nitrate Removing Filter Media

If you have enough space in your filter media, you can also add some nitrate remover pads to help deal with the problem. While this isn’t going to fix the problem instantly, it can definitely help it over time!

As well as these nitrate remover pads, you can also purchase nitrate removal filter sponges as well.

What Plants Are Good For Removing Nitrates

If you want to help keep the nitrate levels low in your tank naturally with plants, then here are some of the best plants to choose from.

Adding any of the following to the tank is going to work wonders in reducing the ammonia, nitrite, and nitrate levels in your tank!

How To Test Nitrate Levels In Your Tank

If you think the nitrate levels in your tank are too high, then there are a couple of things you can do to test them at home.

Paper Test Strips

The first way is to use paper test strips. They are cheaper than the alternatives, but unfortunately, they are also less accurate. To use a paper test strip, remove some of the water in your tank and then dip the strip into it. 

After a few minutes, you’ll be able to tell by the color of the test strips whether the nitrates are too high or not.

Liquid Tests

The second way to test nitrates in your tank is to use liquid test kits. Liquid test kits are a lot more accurate than paper test strips, so you should always choose them over paper test strips when possible.

To use liquid test kits, you just need to take a sample of your water and then add a few drops of the test fluid. Then just give it a good shake and watch the water change color. Once it’s changed color, you’ll know how high the ppm in your tank is.


Here are some frequently asked questions that people have about lowering the nitrates in their aquarium.

Should You Keep A Planted Aquarium’s Nitrates At 20ppm?

It doesn’t matter if your aquarium is planted or not. In both cases, you should keep your aquarium’s nitrates at 20ppm or below where possible.

What Is The Fastest Way To Lower Nitrates In An Aquarium?

The quickest way to lower nitrates in your aquarium is to perform a water change. By removing as little as 20% of the water from your tank, not only will you remove 20% of the nitrates, but you’ll also dilute the ppm even more with the fresh nitrates. 


As you can see, lowering the nitrate in your tank isn’t difficult, and preventing them from rising too high in the first place isn’t difficult either! 

If you liked this article, make sure you check out the rest of the website! Otherwise, have a great day!

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