How Long Does It Take For Nitrate Levels To Go Down?

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Fighting nitrate in fish tanks can be pretty frustrating, especially in new tanks that require cycling. As I suffered from this issue pretty extensively in the past, I decided to dedicate an entire article to this topic.

This is how long it takes for nitrates to go down, depending on the method you choose:

Water conditionersA few minutes
Water changeAs soon as it’s done
Nitrifying bacteriasix weeks

As we move forward, I will share a few tips to help you get rid of nitrates as soon as possible. I will also share the particular conditioner that I use when conducting a water change.

Changing the water will lower nitrate and remove decomposed organic matter.

How Long Does It Take For Nitrate Levels To Go Down?

It depends on what you’ve done to combat the substance. Some people expect nitrate levels in a new tank to drop after six weeks. 

This is because it takes roughly six weeks to successfully cycle a tank.[1] However, that assumption is wrong. 

The nitrogen cycle eliminates ammonia and nitrites. The process introduces bacteria that convert ammonia into nitrates, which are relatively harmless in small quantities.

Therefore, you wouldn’t be wrong in arguing that it takes six weeks for ammonia and nitrite levels to go down

Yet, nitrates are a different case. Unlike ammonia and nitrites, you don’t have to eliminate nitrates from the tank, not completely.

However, to protect your fish, you must keep their concentration below a specific threshold, typically below 20 ppm. Ammonia, on the other hand, shouldn’t exceed 0ppm.

Pro tip: Even though they sound similar, nitrates and nitrites are entirely different substances. Here is an article where I talked all about it.

Some people want to eradicate nitrates. They don’t realize that plants use them as building blocks. Your best option is to lower the concentration. 

If you want to know how long it takes to reduce nitrate levels, a water change will produce immediate results.

This procedure aims to remove some of the water (25 to 50 percent, depending on the severity of the situation), eliminating a significant portion of the nitrates in the process.

Adding new water to replace what you removed will dilute the remaining nitrates, either removing them entirely or bringing their concentration down to manageable levels.

By the time you finish the water change, the nitrate levels should have gone down. How long does it take you to perform a water change? That is how long it takes to lower the nitrate levels.

Nitrate-removing fluids are even more appealing because they work in minutes. Some people use water conditioners that specifically target nitrates. 

Others gravitate towards products that encompass various toxins, including ammonia, nitrites, and chlorine.

Nitrate-removing filter media is less appealing because it can take a while (weeks) to deliver the desired results. This is also true for nitrate-removing sponges.[2]

Plants are an effective weapon against toxins if you prefer a long-term solution.

A 2021 paper in the Ain Shams Engineering Journal identified aquatic plants as a potent answer to pollutants because the right species could absorb organic and inorganic contaminants.[3]

Pathos is a great example. The plant absorbs nitrates through its roots at a surprisingly rapid rate, producing reductions of 20 to 40ppm within five days.[4] 

By eliminating nitrates, the plant will also control the algae population in your tank.

Pro tip: You don’t have to wait six weeks to cycle a brand-new tank. You can use products such as API QUICK START (link to Amazon) that contain pre-made bacteria.

This is the nitrogen cycle that usually occurs in a healthy aquarium environment.

Will Nitrates Go Down On Their Own?

No, nitrates won’t go down, not on their own. A paper in Applied and Environmental Microbiology mentions the strains of Nitrosomonas bacteria that oxidize ammonia.[5]

Another paper in Applied and Environmental Microbiology highlights the bacteria from the Nitrobacter genus that oxidize nitrites to produce nitrates.[6]

People call them good bacteria because they eliminate toxins. However, some newcomers expect these bacteria to consume ammonia, nitrites, and nitrates. But that couldn’t be further from the truth.

The purpose of cycling is to remove ammonia and nitrites. The cycling process is only complete when the aquarium has nitrates in moderate concentrations but no ammonia or nitrites.

In other words, nitrates are a standard aspect of the aquarium, one of those components you expect to find whenever you test the water.

Don’t expect the so-called good bacteria to remove the nitrates as well. Nitrates will only reduce if you take deliberate steps to remove them. For instance, if you perform a water change

If you haven’t done anything and your tank doesn’t have nitrate-removing filter media or sponges, the only logical culprit is your aquarium’s plant population.

Plants consume nitrites and nitrates. Therefore, if you have a decent collection of aquatic plants, the nitrate levels will appear to go down on their own. 

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

It depends on who you ask. Some people think water changes are the fastest solution. But that depends on how long it takes you to perform a water change. 

Rationally, water conditioners should be the fastest tool because they can lower the nitrates within minutes.

They will either turn the nitrates into nitrogen gas or neutralize their toxicity. Then again, some people perform water changes within ten minutes.

If it takes you an hour, you would be right in identifying water conditioners as the fastest solution. 

Most professionals will encourage you to prioritize water changes. Conditioners are a band-aid. They can lower toxins during emergencies. 

But a water change removes the elements that attracted the nitrate spike, including dead plants and leftovers. It cleans the tank, creating a more conducive environment for your fish.

There is plenty of debris within the aquarium substrate that consistently rots and produces toxins.

Why Won’t Nitrates Go Down With A Water Change?

How do you know the nitrates have refused to go down despite the water change? One assumes that you tested the water. But do you trust your testing kit?

Believe it or not, testing kits can expire. Others have factory defects. Confirm your suspicions by purchasing a new kit and testing the water again. 

Better yet, try a different method. For instance, if you typically use strips, experiment with liquid tests. You can also send a sample of aquarium water to a lab for confirmation.

For more information, here is an article where I explained how to test for aquarium nitrate. You will find it extremely useful if you are new to this topic.

If you know for a fact that your tank’s nitrate levels are still too high despite the water change, the water change is the problem. 

If you find that hard to believe, consider this study from the International Journal of Environmental Research and Public Health which has warned readers about the increasing concentration of nitrates in water resources.[7]

If you trust the water in your tap enough to drink it, you probably thought it was safe enough to add to the aquarium.

But if that water source has high nitrate levels, each water change will add to the nitrate concentration in the aquarium instead of reducing it.

Many aquarists use conditioners to remove chlorine and chloramine from tap water. It doesn’t always occur to them to apply conditioners that remove nitrates. These products also neutralize ammonia pretty efficiently.

Which Water Conditioner Should I Use To Combat Nitrate?

As discussed earlier, water conditioners are an excellent solution when detecting toxins in your tank, including ammonia, nitrite, and nitrate.

But not all water conditioners work the same. Some focus on elements like chlorine and chloramine while ignoring other important toxins.

The product that I typically recommend is the Seachem Prime Fresh and Saltwater Conditioner (link to Amazon).

This conditioner works in several ways:

  • It removes chlorine and chloramine from tap water.
  • It detoxifies ammonia and nitrite, and by that, it lowers nitrate turnover.
  • It clears heavy metals typically found in tap water.
  • It enhances the nitrogen cycle that usually takes place in the biofilter.

To make this happen, all you have to do is to use 1 capful (5 mL) for every 50 gallons (200 L) of new or replacement water:

Pro tip: Dealing with ammonia is key when you find high nitrate levels in your tank. Here is an article with all the information you need about ammonia, including the specific products I use to remove it.

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If you detect a nitrate spike in your tank (40-50 ppm and higher), the fastest way to lower it would be using a water conditioner. These products usually work within minutes.

However, they lack the advantage water changes have as they don’t remove the elements that caused the toxin to form in the first place.

That is why the two solutions go hand in hand. Don’t rely solely on a water conditioner, otherwise, the toxins will spike again in the next few days.

If your tank is still new, nitrates won’t go down on their own. You’ll have to cycle it for about six weeks, which is how long it takes for nitrifying bacteria to form.