nitrate levels in saltwater aquarium

How to Lower Nitrate Levels in Saltwater Aquarium? and What are the Acceptable Levels

Acceptable nitrate levels in saltwater aquarium are an important topic that most people don’t give much thought to. However, these nitrates can have major effects on the health of your fish and other inhabitants. There are many things that can cause high nitrate levels in a saltwater aquarium, but there are also preventative measures you can take to lower them before they get out of control.

In this article, we’ll cover what acceptable nitrate levels for a saltwater tank is, how to determine or test whether your water has high concentrations or not, how to lessen the effects of elevated nitrates and steps you should be taking if you do find yourself with high levels of nitrates in your saltwater aquarium.

acceptable nitrate levels in saltwater aquarium
Image Source: bulkreefsupply

What is Nitrate and why does it matter?

Nitrate is one of the three main nutrients that are essential for plant life. Although plants require nitrates to grow, too much nitrate can become problematic in an aquarium environment if it isn’t controlled by water changes or filtration methods. Nitrite and ammonia are other nitrogen compounds found in saltwater aquariums which both need to be monitored in order to keep a healthy saltwater aquarium.

Nitrate is not directly harmful but it can be the byproduct of other compounds in your tank which are dangerous if too high. Nitrates themselves will cause algae to grow faster and more prolifically. This excess algae growth may clog filters causing them to lose their efficiency over time because they need to be cleaned regularly. The nitrates can also suffocate coral reefs when concentrations get really high enough that you could see visible signs within just 24 hours without appropriate intervention.

Sources of Nitrate

You may add nitrates in your saltwater aquarium without even having any idea as to how you did it. It can be from a number of sources that are inherent in your aquarium ecosystem. Nitrate (NO) enters the system through two sources: the nitrogen cycle & water changes.

Water evaporates from your aquarium’s surface, condenses in the atmosphere then falls back down as rain; carrying with it atmospheric Nitrogen that eventually dissipates into ground-level waters where algae can use this source of Nitrates for their growth cycle. The second way nitrates enter an aquarium is via new livestock or water changes are done on a routine basis because they bring along extra nutrients coming out of solution within these systems themselves.

Over time these levels will start building up in your aquarium’s water column and eventually reach critical concentrations where algae can take advantage of this source which is why nitrates should be monitored carefully because once the level starts getting too high at some point there won’t be anything else left but algae for it to feed upon.

Nitrogen Cycle how it works

One way that saltwater fish and invertebrates produce waste is through their gills as they extract Oxygen for survival. This process also occurs in your aquarium when you add new livestock or perform water changes because these organisms are adding additional Ammonia and Nitrite into your tank’s ecosystem.

Before we get too far ahead of ourselves though let’s first discuss what happens after this formaldehyde-like substance starts building up within the system itself. Fish release ammonia (NH) directly into their surrounding environment by excreting uneaten food, decaying matter such as dead skin cells, etc. Ammonia is highly toxic to fish and invertebrates which is why it must be monitored closely.

The acceptable nitrate levels in Saltwater Aquarium

the acceptable range of nitrate for a saltwater aquarium may differ from a freshwater aquarium as saltwater fish can survive at higher nitrate levels as compared to freshwater fish.

For a fish-only saltwater aquarium, the ideal levels of nitrate are from 10 ppm, but levels up to 40ppm will not cause harm.

However, for a reef system, acceptable levels are between .25 ppm and 5 ppm as the corals, anemones, some crustaceans, and invertebrates are really fragile and delicate to survive in high nitrate levels.

You also do not want to see signs of algae growth because this is one sure sign that nitrates have exceeded acceptable levels already even though they may still remain unnoticeable at lower ranges up until very recently before those effects become apparent.

How to To Test Nitrite Levels In Your Aquarium?

Your best bet when it comes to testing your reef system water quality at home is to purchase simple nitrate test kits from your nearest pet store which should have kits available that range from ammonia, pH, alkalinity/acidity, phosphate, and nitrite/nitrate tests.

Testing often will help keep track of any changes in these parameters so you can take corrective measures as needed before things get out of hand.

test kits for testing nitrate

How often should you test nitrates?

It’s best to monitor and check nitrate levels on a weekly basis especially if your tank is heavily stocked with fish/coral, if not daily! If the results show that they’re elevated above acceptable ranges then please be sure to take corrective action immediately as this can lead to an array of undesirable consequences which we’ll discuss below.

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The effects of elevated nitrate in saltwater aquarium

A level above 40ppm will start to show signs of stress, including pale gills and a lack of appetite. At 70-80 ppm, the fish may lose their appetites completely and stop eating which can lead to much worse problems such as:

  • ammonia poisoning or mouth fungus due to malnutrition
  • gasping at the surface for air
  • skin discoloration
  • disease outbreaks such as fin rot.

If your reef system is experiencing high nitrates then algae growth may become out of control leading to an increase in phosphate that further complicates matters by encouraging nuisance algae like cyanobacteria (red slime algae). Another side effect for coral reefs is decreased growth rates of their calcium carbonate skeletons.

Common Causes of Higher Nitrate levels in Saltwater Aquariums

Generally, there are three main sources of nitrate that lead to high levels in saltwater aquariums. Nitrates can be introduced into your saltwater aquarium via the fish you add, the foods they eat, and how well your filtration system is able to handle waste removal. However, it is important to note that oftentimes these issues will compound upon each other and create much worse problems than originally expected.

the most common cause of higher nitrate levels is as already stated and the most common causes of organic waste in your saltwater aquarium are:


The most common source comes from overfeeding – often it seems like our fishies need more food when in fact, what we’re actually doing is polluting their home! In between regular feedings, give them some time without feeding so they don’t have leftover bits all around which will cause algae growth and increase nutrient loading from decaying food.

If you have to feed more than once per day, be sure to only give them the amount they can eat in about five minutes or so and remove any excess food after that time has passed. If your fish refuse a portion of their meal, don’t try to force it onto them because this will also cause even higher levels of nitrate which leads us into our next most common culprit… overstocking!


A good rule of thumb is not to put more than one inch (per gallon) of adult fish inside your aquarium.

You may be tempted to fill your aquarium with as many fish as you can, but this will greatly increase the amount of waste that needs to be processed through their bodies and also increases how much excess food they need. If you want a very full-looking tank without overcrowding it is acceptable to have ten inches of adult fish per every fifteen gallons because we do not count “hiding” spaces like plants or rocks in our calculations.

polluted water filters

Polluted water filters will also cause you to have higher nitrate levels because the filter media has been broken down and is not performing its job as well.

underdeveloped denitrifying bacteria

One of the main reasons for elevated nitrate levels in a saltwater aquarium is that your biological filtration (nitrification) hasn’t developed fully yet. This can be caused by several factors, but these are some major ones: an inadequate surface area within the tank; too much organic waste; lack of oxygenation; or if there aren’t enough beneficial bacteria available such as from under-filtering your source water with activated carbon or using aged/stale rock before putting into an established system.

How to Lower Nitrate levels in saltwater aquarium?

Nitrates can be controlled by regular partial water changes (20% every two weeks) and supplementing your tank with live rock rubble which will help facilitate denitrification, a process where bacteria on the rocks convert nitrogen compounds into inert gases like N₂ gas. This helps lower nutrient loading within the aquarium system so it won’t cause any unwanted algae growth or lead to poor coral health/growth rates down the line! The key is to ensure the rock rubble is “aged” or has been curing for at least three months before adding it into your aquarium.

Add Mangrove plants

The key factor in controlling or lowering high nitrate levels is heavily correlated to how you take care of your aquarium. the use of mangrove plants to control nitrates is an old method and is still used by many saltwater aquarium hobbyists out there!

Mangrove plants are known for how efficient they can be at removing nitrates from their environment and will do it with ease. For this, you’re going to need a mature mangrove plant (which is best achieved if the roots of these plants aren’t exposed) or one that has been “dropped” naturally in your tank during its early stages; this ensures the plant isn’t dying/thriving off high nitrate levels but rather reducing them through natural survival methods. To keep up nitrate reduction efforts on a daily basis, ensure you have between three and four mangroves within your system.

mangrove plants
Image Source: pxfuel

 Replace aquarium water periodically

As mentioned before changing waters regularly reduced the dangers of higher nitrate levels; how often you change your waters depends on how nitrate levels are in the tank. If they’re low, water changes of 50% weekly will suffice; if they’re high (over 40 ppm) it may be more beneficial to do 15-20 percent daily or even hourly until these levels reach an acceptable level for living inhabitants.

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Natural Nitrate Reduction (NNR) Filtration Setups

when setting up a saltwater aquarium or a reef tank is to add natural nitrate reduction filtration setups that can be of three combinations. the idea is that nitrifying bacterias naturally reduce the high nitrate levels. the three setups you can choose from is

  • use live rock
  • live sand
  • live rock and live sand both

Biological filtration is the best way to reduce excess nutrients in a saltwater aquarium. Nitrates are reduced through beneficial bacteria that live on rocks and other surfaces within your aquarium system, which feed off of nitrate as their primary food source.

The more surface area for this type of bacterial growth you provide inside of your marine life environment will lead to a greater rate at how fast nitrates can be broken down into free nitrogen gas molecules again before they start causing harm to too many algae or coral tissue within your display tank setup. If using rock make sure it has been cured properly prior to adding it with any living organism present so do not add anything new until after one month from when all water parameters have stabilized completely yet still keep up on your water change schedule.

Water change schedule

Hiatt’s Right Now! (RN!) and Carbon

Hiatt’s right now is a blend of organic compounds that increase oxygenation, provide energy sources for denitrifying bacteria, and inhibits the growth of ammonia-oxidizing organisms. this product along with carbon will help lower nitrate levels n a saltwater tank by 60-80 percent over two weeks time. This has been proven scientifically using erythromycin as a nitrate control method which showed how Hiatt was able to significantly reduce nitrates without killing all life within the system itself. A 50/50 mixture between RN! and activated charcoal should be placed into an active area where it can break down harmful nitrogenous wastes.

Aeration and Effective filter installation

Aeration and filtration systems can also reduce nitrate levels in a saltwater aquarium. Nitrates are generally removed from the water column by increasing surface area, which provides necessary Oxygen for aerobic bacteria to break down Ammonia into Nitrite then eventually into less harmful Nitrogen gas as it is released back into the atmosphere as waste material.

In addition, an increased amount of aerobic bacteria will help break down organic wastes within your system using oxygen that has been pumped through your filters or other means. A good amount of this beneficial type of bacteria can be found in many products sold in pet stores such as bio balls and ceramic rings on equipment like fluidized bed reactors (FBRs). These tend to work well with larger tanks, but smaller systems can benefit from the addition of live mangrove plants to help increase nitrification.

filters in saltwater aquarium
Image Source: Amazon

Sump filters

A sump filter could also provide another option for removing nitrates but it needs to be big enough so there are no dead spots where detritus may accumulate because remember what goes in doesn’t always come out immediately.

Using Denitrator Units, Absorption Compounds, and Additives

another effective yet expensive way to lower nitrate levels is through using denitrator units. These can be purchased at most aquarium specialty shops will work well for tanks of over 100 gallons. Absorption compounds are also effective in removing nitrates, but they do not remove phosphates which can lead to algae blooms if left unchecked.

Pump water through phosphate removal media or resins before adding it back into your tank. Yet another option is pumping the source water through a simple filter containing either activated carbon or zeolite powder prior to reuse within your system. This removes some of the excess nutrients from the newly added saltwater that could potentially cause an algae problem down the road once again. Always remember when using any type of chemical additive with marine life present how much you add must always be less than how much makes it to your tank.

Image Source: Bulk Reef Supply

Collect organic waste with a protein skimmer

A protein skimmer is a great way of controlling nitrates as it lowers waste products in a saltwater tank. Nitrate levels tend to rise in the early stages of a new tank while it is cycling. A protein skimmer can help remove these excess nitrates and other organic waste products which will aid in keeping your aquarium healthy for its inhabitants.

Use natural algae eaters like hermit crabs or snails

Hermit Crabs could be another option when controlling nitrate levels. Another thing you need to consider is how many should I add to keep up with cleaning the tank? Depending on how large your system is, if you have multiple tanks then placing them together would work great as well so they can clean each other’s shells. It’s also important not to overfeed these scavengers otherwise they’ll be taking away the nutrients your live rock needs.

Image Source: flicker Matthew Paulson

grow macroalgae in a refugium

Another way to control how much nitrate you have in your tank is by growing macroalgae. This would be done in a separate filter called the refugium which will act as an algae farm that can help remove excess nutrients from the water column.

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There are several species of macroalgae that do well under high light and nutrient conditions such as Chaetomorpha, Caulerpa, or Gracilaria lemaneiformis.

Image Source: myreef.aquariumdepot

Stop Overfeeding and Overstocking

yes, overfeeding and leftover food are some of the main sources of nitrates so as much as this sounds cliché you must create a feeding pattern for your saltwater aquarium to avoid overfeeding while avoiding overstocking by not adding too many fish to your aquarium

Set up a Sulfur reactor

another way to reduce nitrate levels in your saltwater aquarium s by setting up a sulfur reactor. a sulfur reactor filters the nitrogen through sulfate-reducing anaerobic bacteria which will convert ammonia to less harmful nitrates in a saltwater aquarium. Moreover, the sulfur reactor will also act as a refugium to help grow macroalgae that can be used for nutrient export.

Use of RO/DI water

Last but not least, using reverse osmosis or deionization (RO/DI) water provided by commercial fish stores is recommended though the use of an RO/DI system might come at an extra cost so it’s always best if your tap provides good quality drinking water. Of course, ensuring a high-quality and clean source of tap or well water should be done regularly for this purpose too. It would be advisable to check out with local government agencies regarding how often water testing should be done in your area.

Use Deep Sand Beds

One of the most effective ways to remove unwanted nitrate from your reef tanks is by using a deep sand bed (DSB). It is a layer of sand situated at the bottom part of your tank. What makes it different from other substrates in your aquarium? It has a much larger surface area due to how fine and deep its grains are. This gives more room for bacteria colonies to grow which will help break down nitrate into harmless nitrogen gas that gets dissolved in water then released out through the air or by denitrification where they get converted back into their gaseous state.

A DSB’s depth should be about two-thirds of your total tank volume with an approximate minimum thickness of six inches (15cm). The best way is to use a container such as a fish box or bucket when filling up sands.

Image Source: Youtube RMSpeltz Farm

pre-made DSB

The next option is to purchase a pre-made DSB that you can simply pour into your aquarium. These are generally made from pressed plastic, glass, or other materials designed for marine use. They have various forms of internal structure but they all create the same effect as any DIY version with how their grains are arranged and how deep it extends down. Again, six inches (15cm) should be near enough depth before starting anoxic conditions in your tank to let denitrification begin breaking dissolved nitrate down completely by using aerobic bacteria colonies to transform them over time.

This process takes longer than carbon dosing because once these colonies start converting ammonia into nitrite then into lower levels of nitrogen compounds like nitrate; they will also produce waste which can affect how clean your water is so it’s best to keep an eye on these levels if you decide not to put any live rock in your tank.

Use Nitrate Remover:

Use a nitrate remover to suck up any excess sediment and to make sure your water stays clean. a nitrate remover will help to keep your water clean and will also allow the bacteria colonies in your saltwater aquarium filter to work overtime without being disturbed.

Nitrate removers are designed just like any other type of filtration system that you have set up for your fish tank with a pump, tubing, chambers, sponges, or pads that hold activated organic carbon which then traps nitrates when they pass through this chamber so it’s best not to disturb them when cleaning out waste since these beneficial bacteria can be easily damaged by sudden changes in pressure or temperature which means disturbing how well they convert toxic ammonia into less harmful forms of nitrogen compounds.


Setting up a saltwater aquarium and maintaining one is quite a task. If you’re doing it for the first time, take your time and do some research. If you are unsure how to proceed, take your time, make sure everything is working properly, and then only move on.

controlling nitrate levels is one crucial element in keeping a healthy saltwater aquarium. A tank will quickly become toxic if the water quality becomes imbalanced, which can be easily avoided by maintaining proper nitrate levels as discussed above.

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