In all fish systems, your nitrogen cycle is hard at work converting harmful ammonia and nitrite into safe nitrate. Nitrate is commonly removed from your system by water changes or live plants in freshwater systems or algae in saltwater systems, usually in a refugium. But what are you to do if neither is an option?
The following products work by removing nitrate from your saltwater aquarium system mainly by converting the nitrate to another, less toxic form or binding it in another area of your aquarium. Keep in mind that some products will not completely erase your nitrates, but bind them for a certain period of time. Once a product is used up in your tank, you will need to replenish the supply or your system will start having a build up of nitrate that can seriously affect your fishes’ health. Depending on your tank’s species and ages, some may be more sensitive to nitrate than others.
Products have varying mechanisms of action, attacking the nitrate problem from various angles. Depending on your tank setup and budget, one of these options may work better than some. For all reef and saltwater systems, be sure to read the packaging carefully for dosing and suggested additional equipment, such as protein skimmers. You may need to try various products to find one that works best for your system.
Ahead, the best nitrate reducing products for saltwater aquariums.
Seachem Purigen Organic Filtration Resin
Color-changing when used up
Can replace carbon filter
Can be messy
Needs retaining system
SeaChem Purigen is a synthetic absorption resin made up of a macroporous polymer. It is a slightly messy material, so it is recommended to be kept in a mesh bag. Some Purigen products come ready-to-go in a bag. Purigen needs to be replaced regularly, but you will know when depending on the color of the material. Starting out white, the polymer will change color depending on what is being scrubbed from the water. After the material is no longer white, it will need to be replaced. You may get a few uses out of one bag by recharging it in a mild bleach solution. Some hobbyists use Purigen instead of carbon and it will act similarly, deactivating any water-based medication added to your tank.
Purigen is safe for use in both saltwater and freshwater systems.
Price at time of publish: $12 (100 ml)
Best Overall Runner Up
DrTims NP-Active Pearls for Nutrient Control
Best researched product
100 percent safe for fish
Requires protein skimmer or additional filter
DrTim’s Pearls are a slowly degradable polymer that provide a carbon source to nitrate-reducing bacteria, similarly to Red Sea’s NO3:PO4-X. This product acts as a food source for bacteria you already have in your tank that utilize nitrate as a food source.
However, feeding bacteria can produce a bacterial bloom and hurt your tank’s biodiversity and cause thick bubbles from protein waste. Therefore, a protein skimmer or additional filtration is recommended to keep your tank from becoming bacterial soup. As with the SeaChem DeNitrate, this product requires a “reactor” level of water flow for proper utilization and breakdown of the contained polymer. Some hobbyists have good results adding this to their fluidized bed filter, where constantly moving water provides good water flow.
Price at time of publish: $33 (16 ounce)
Seachem Denitrate 1 Liter
Simple to use with no additional additives or products
Paying extra for fancy rocks
SeaChem DeNitrate is essentially rocks that work similarly to any live rock you have in your system already. These rocks work by providing housing for anaerobic bacteria who use nitrate as a food source. It's important to remember that De-nitrate is going to be most helpful for long-term maintenance of nitrate levels, and won't help as much in an acute crisis.
In order to properly function and get the most conversion for your rock surface area, the water flow through the product must be at a specific level. This is one of the hardest factors to control within the aquarium itself, so some users recommend adding this to a filtration element. If the water is moving too fast, nitrate utilization by the resident bacteria will not be very efficient, and if it is too slow, the bacteria will die without access to their food source. Overall, if you already have live rock, save yourself the money and skip these fancy rocks.
Price at time of publish: $21
Red Sea NO3:PO4-X
Treats both nitrate and phosphate issues
Same as vodka method
Requires protein skimmer or additional filter
Red Sea NO3:PO4-X is specifically designed to treat both nitrate and phosphate overload in coral tanks with algae issues. It works by providing additional supplementation for heterotrophic bacteria that utilize nitrogen and phosphate as a food source thereby naturally removing it from your system. However, with the supplementation of these bacteria comes a secondary bacterial bloom. Therefore, it is highly recommended to use this product with a protein skimmer to remove the additional proteinaceous bacterial load.
Keep in mind that the main active ingredient, ethanol, is highly flammable, so store this product in a safe place and keep it away from children. This product works very similarly to the “vodka method” to reduce nitrates.
Price at time of publish: $32
DrTim's Aquatics One and Only Live Nitrifying Bacteria
Can be used in new or established tanks
Comes in a wide variety of sizes, suitable for both small and large aquariums
Nitrifying bacteria products may not work
Nitrifying bacteria products—which add bacteria that convert nitrite and ammonia into non-toxic chemicals—sound like a great idea, but have a number of variables which make it hard to determine how will they will work in your tank. Bacteria products commonly die when not stored properly, or maybe the specific blend of bacterial species won't thrive in the specific ecology of your tank. You can read more on nitrifying bacteria products here.
If you'd like to try out a nitrifying bacteria product in your tank, then we recommend DrTim's Aquatics One and Only Live Nitrifying Bacteria. We tested it alongside several other nitrifying bacteria products and found that it was only the brand that produced any effect at all—a measurable change to the nitrogen cycle in our test tank.
Price at time of publish: $16
For those just getting started with an aquarium SeaChem Purigen is simple to use and great for beginners. For a budget option, SeaChem DeNitrate is low cost and doesn't require any extra equipment.
What to Look for in a Nitrate Reducing Product
How Do You Know If Your Product Is Working?
Various nitrate reducing products will utilize different methods to indicate if they are working. Some will change color, while others will slowly shrink. If you are unsure about how a product will be used in your system, you will need to continuously check your nitrate levels.
Depending on the product you choose, you may need to continually dose your system or just add as needed. Be sure to read the instructions carefully and take dosing into any financial considerations.
Some products work by boosting bacterial colonies, which can cause other problems with your water quality and biomass. Protein skimmers are a common feature of saltwater aquariums, but may need to be added for some of the recommended products and cleaned more frequently.
Reusing Various Products
Some of the recommended products can be reused if they are recharged. Some freshwater products actually use saltwater to be recharged, and therefore are not able to be utilized in marine tanks. Some products can be recharged in a mild bleach solution per the manufacturers instructions, making them a better investment.
Saltwater vs. Freshwater
Read all the fine print before purchasing a nitrate reducer. Some products are very specific to only one type of system. As mentioned previously, some products are recharged using salt water, making them only effective in freshwater systems.
Can you reduce nitrates in saltwater aquariums without changing the water?
There are many mechanisms available to a saltwater aquarium owner to remove harmful nitrates from their aquarium system. Nitrate reduction without water changes is critical to those hobbyists who do not have great access to clean source water or lack the physical ability to heft large buckets of salt water.
Keep in mind that water changes remove more than just nitrate. Biological products from your fish, including hormones for stress and reproduction can also build up and may need to be removed through water changes. Unfortunately, there are no tests available for these on the commercial market.
Do aquarium plants reduce nitrates?
In freshwater systems, yes indeed, plants can reduce nitrate levels. However, most live plants do not survive in saltwater systems. For saltwater systems, macroalgae can help remove nitrates from your system in a similar fashion.
Most of these filtration units are set up in a refugium. This is a separate chamber of your filtration that houses macroalgae and some invertebrates, if desired. The amount of plant or algae will help with nitrate levels, but do not expect it to do all the work unless you have a considerable amount of macroalgae or plants.
"Macroalgae may present an interesting option for some hobbyists, especially considering the recent trends towards natural and low-maintenance systems," says Dr. Ashley Emanuele. "The term macroalgae is applied to a large group of multicellular seaweeds, and they are often maintained in a refugium or sump. Adding additional light and powerheads to the refugium allows the algae to act as a natural sink for nitrate products, similar to the way plants function in freshwater aquaria."
Does charcoal reduce nitrate levels in an aquarium?
Activated carbon, used as a water purifier in both saltwater and freshwater aquariums, does not impact nitrate levels in either type of system. Carbon will remove chloramine, carbon, tannins, and phenols, but will not remove any nitrogen products, including ammonia, nitrite, and nitrate.
How do you know if a nitrate reducing product is working?
Depending on the product you are using, some may change color to demonstrate that they are working. However, the best method of verifying nitrate levels is to test your water chemistry using a liquid-based test kit. Be sure to read all testing instructions carefully, shake your testing bottles thoroughly, use them regularly, and replace them every year.
Why Trust The Spruce Pets?
There are many products on the commercial market that are targeted to make your aquarium maintenance easier, but do they really come through? The following products and their mechanisms were scrutinized by Dr. Jessie Sanders, an aquatic veterinarian with over eight years experience working with pet fish and four years in the public aquarium industry. She also consulted with Dr. Ashley Emanuele, who is a Certified Aquatic Veterinarian.