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How to Lower Nitrate levels in Saltwater Aquarium

Nitrates are the end product of the nitrogen cycle in your aquarium. While it is correct that nitrate is the least harmless chemical component of your saltwater aquarium, certain quantities may pose a challenge to your tank and fish. Aquarists tend to go all out to combat ammonia and nitrite but become lax when it comes to nitrite; this is a big risk.

This article provides an expose on the dangers of underestimating the presence of nitrates; and provides useful tips on how to lower the level of nitrate in your saltwater aquarium. Before sharing this, it is imperative to define the terms that constitute the subject matter, the causes of high nitrate levels in saltwater aquaria; as well as the consequences of a nitrate level surge in your aquarium.

Understanding the Issue

Salt water’s distinctive feature is evident in its name: it contains a high level of salt. An additional feature is that saltwater is denser than freshwater. The Earth is 97% saltwater and 3% freshwater, and saltwater fish vary in anatomy and physiology from freshwater fish.

Typically, saltwater fish cannot survive in freshwater because their body is in constant need of replacement of the internal body fluids that they lose as a result of osmosis. By consuming large amounts of saltwater, they replace these fluids. Coral reefs, oceans, deep seas, lakes, mangroves, and seagrass beds are sources of saline water (also saltwater)

This article’s spotlight is on how to lower a high nitrate level in your saltwater aquarium if you’re experiencing that. If you are not, this article will inform you of how to keep nitrate levels in control, so follow along!

Effects of Surge in Nitrate Level

Nitrate is the broken down version of nitrites by beneficial bacteria in your aquarium and is not to be dismissed as non-toxic; it causes problems to your fish in these areas if not well curbed:


High levels of nitrate can affect the growth of young fish especially. If you have not been checking and monitoring the nitrate levels in your aquarium, you may want to get to it now to avoid slowing down the biological development of your fish. 

Algae bloom

Algae feed on nitrates; and if your aquarium is full of them, you are inviting algae to your saltwater tank. Algae infestation is one of the biggest problems potentially facing any saltwater aquarium; not only do they give an unsightly outlook to your tank, but algae also pollute and eventually kill aquatic plants and animals.

Algae bloom

Algae feed on nitrates; and if your aquarium is full of them, you are inviting algae to your saltwater tank. Algae infestation is one of the biggest problems potentially facing any saltwater aquarium; not only do they give an unsightly outlook to your tank, but algae also pollute and eventually kill aquatic plants and animals.

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Blotch Break-outs

If no precautions are taken, fish exposed to nitrate at high levels, for some time, may begin to fester sores on their skin and become very lethargic; this condition is known as nitrate poisoning.

The reason behind the Issue

The presence of concentrated nitrate in your saltwater aquarium will affect the psychology of your fish. This is as a result of the destabilized oxygen levels in your tank commonly caused by nitrates.

With inadequate or unstable flows of oxygen, your fish stand the risk of falling sick or worse. Your aquarium and its inhabitants are meant to bubble with life, not be torpid.
The effects of accumulated nitrates can be as dangerous as the smallest quantity of ammonia and nitrites. This begs the question of what causes nitrates to accumulate in saltwater aquaria.

Cause of Nitrate Accumulation Cause

Certain habits contribute to the rise of nitrate levels in your saltwater aquarium and unlike its predecessors in the nitrogen cycle; nitrate is harder to physically detect.

It is odorless and does not affect watercolor or physical features. Hence, it is important not to always assume that all is well in your aquarium.

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A surge in nitrate levels is usually a result of one or all of the following:

Overcrowding your saltwater aquarium

When your fresh water tank is overfilled with fish, it becomes increasingly difficult to keep up. Too many fish in release too much waste than your aquarium can handle and the end product of the nitrogen cycle is a staggering level of nitrate.

To avoid this problem, ensure that you only have a minimal number of fish in your aquarium at a time; and according to the size of your tank. If you must add more fish, we highly recommend that you purchase a bigger tank. Consequently, your fish have enough space to move around and you can monitor their activities easily.

Excessive feeding of fish

This is linked to the first point, but even a few fish can be overfed. Perhaps in a bid to give your fish the best care, you go over the top with food rationing. Your intentions are noble but you are doing more damage than good to your fish and your aquarium as a whole.

Excess food left uneaten will significantly add to the quantity of waste in your water. Apart from risking an increase in nitrate levels, your aquarium becomes prone to an algae bloom.

Rotting Plants and Leaves

It is correct that aquatic plants absorb nitrate as an essential nutrient, however, if these plants, especially their leaves dry out and fall; they begin to decompose and if not immediately evacuated, they add even more waste to your water. This build-up of toxic waste results in high nitrate levels.

Insufficient maintenance checks

This is another common cause of nitrate booms, caused by undermining the potential danger of nitrate. This coupled with laxness in carrying out maintenance tasks such as cleaning your filter and changing water. A dirty water filter and stale water will shoot up the nitrate level in your aquarium.

Nitrate Levels

As a beginner aquarist; or one that is just getting to know about the dangers of high nitrate levels in the water, you must be curious as to how much nitrate is manageable and at which point you should get concerned.

Some websites will inform you that nitrate levels below 100ppm are relatively safe and nothing to worry about, but we recommend that you treat your water once the nitrate levels rise to 30ppm to 50ppm.

Ideally, nitrate levels should be kept below 10ppm; therefore, you may pay it no mind if it is on 15ppm or 20ppm; anything above that calls for immediate attention to prevent the situation from spiraling out of control.

Keep a close watch on your saltwater aquarium using original home testing kits, and take safety precautions on time to prevent the surge.

How to Lower Nitrate Levels in Saltwater Aquarium

Water Change

If your aquarium is saltwater, the most effective means to lower the nitrate level in your water is by changing your water; partial water change. The process of water changing is one of the most important maintenance routines in the aquascaping hobby.

Water left unchanged become stale as a result of the chemical and biological activities going on in it. It is also the easiest way to get rid of that entire nitrate. The logic is pretty simple; you get rid of the water, you get rid of the nitrate therein.

But before you get to it, take note of the word ‘partial’; that means you do not get to pour out all the water in your tank and refill it with new water. Why? - For all your creative needs!

We earlier discussed saltwater fish and how selective they are regarding habitat. Fish; saltwater and freshwater fish alike, are very sensitive to change. This means that they are immediately aware of the slightest changes in their habitat such as water chemistry and temperature, and they react to it extremely.

Suddenly changing the water they live in can kill them. There is toxic nitrate in the water, but in a bid to save them and your saltwater aquarium, you have to follow a procedure so you do not wind up causing more harm to the fish. When changing your water whether as a maintenance routine or to rid your saltwater aquarium of nitrate, you are only expected to change a part of your water; typically not more than have.

A partial water change to remove nitrates is also done in phases: lightly vacuum your substrate and remove only about 15% of the water per day and refill with new saltwater. Continue this until you have removed about half the water; this dilutes your saltwater and reduces the nitrate level drastically, without shocking your fish.

Addition of Aquatic Plants (Mangroves)

Adding plants to your saltwater aquarium is a biological method and an old trick that will prove quite effective in the reduction of the nitrate level in your water; aquatic plants such as mangroves will make a great visual addition to your saltwater aquarium and relatively lower nitrate level.

It is, however, important to note that plants can only take in the number of nutrients that they need per time. In the case of excessive nitrates available, this step may not be as effective as outright water changes.

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Use of Natural Nitrate Reduction Filter

This method involves the use of organic hardscapes such as sand, rocks, or both in your aquarium. In effect, nitrifying bacteria (or beneficial bacteria) from these hardscapes act on the nitrates and break them down into less harmful quantities. Note that this is more of a preventive measure than a solution.

The aforementioned steps; notably water change tops the list as a very reliable, easy, and potent means of curbing the rise of nitrates levels in a saltwater aquarium. To keep up with the activities of the nitrates in your aquarium,

Purchase original home testing kits from a credible supplier to monitor water PH, ammonia, nitrite, and nitrate levels in your saltwater aquarium
Keep a daily record of measured levels of nitrate and observe the rise. If it needs preventive measures, be proactive, and take them.

Study the nitrogen cycle and its effects on your saltwater aquarium before adding aquatic plants to your saltwater aquarium, ensure that they compatible with your fish and they serve the purpose of regulating nitrate levels

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Nitrates are a natural part of your saltwater aquarium, and as long as you keep it check by following the steps given in this article, you are prolonging the life span of your fish, plants, and aquarium environment. It is worthy of emphasis that either as a fish keeper or aquarist or aquascape hobbyist, research is needed for every method you employ and every step you take.

Saltwater aquariums are slightly different from those of freshwater; study those to get a solid knowledge of how to handle your aquarium. A healthy aquarium not only creates a happy environment for your fish and plants, but it also makes the aquarist happy and fulfilled. If you try one method and it doesn’t yield the desired results, try other methods until the problem is solved!