The final by-product of fish waste and the cycling process in a saltwater aquarium is nitrate.

Having high nitrate levels in a marine/reef aquarium can lead to many problems. Nuisance algae growth, a decline in coral health (loss of color/growth) and fish/invertebrate illness or death are all possible if you allow your nitrate levels to rise to dangerous levels.

But you'd never allow THAT to happen, right?

As a responsible reefkeeper, you want to keep your nitrate levels as low as possible. You also want to accomplish that with as little effort as possible. Well, today is your lucky day!

We have discovered six simple tricks to control nitrates in a reef aquarium. We are confident if you employ one or more of these methods you will be able to successfully lower the nitrates in your tank and be on your way to a happier, healthier reef.

Make water changes and vacuuming substrate easy with a siphon and hose.


Don’t act shocked. Of course water changes are going to make our list.

Performing large weekly water changes in the 20-40% range can go a long way toward reducing the nitrate level in a saltwater aquarium. However, you must be certain the water you are adding back to your tank is nitrate-free.

We strongly encourage you to use filtered water (like RO or RO/DI) to mix saltwater for water changes and tank top-off. Test your water change water with a nitrate test kit before you add it to your aquarium to make sure it is nitrate-free.

If you continue to perform these larger water changes regularly with nitrate-free water, you will most likely see your nitrate levels drop within acceptable levels within a couple of months, if not sooner (it depends on your starting level).

Remove excess nutrients before they enter your tank with a fish food strainer.


We would all love our reef tanks to teem with life around every bend. But overstocking your aquarium can be a real problem.

If your tank is so overcrowded with fish that filtration equipment and regular maintenance can't keep up, we urge you to consider reducing the number of residents in your tank.

Increased bioload isn't the only problem livestock face in an overstocked tank. Animals also have to contend with each other in close quarters, which can lead to stress, aggression, lack of exercise and increased competition for food and habitat.

Overstocking and overfeeding often go hand-in-hand, but not always.

Feeding time is when the entire aquarium comes alive: nassarius snails burst from the sandbed, crabs scuttle out of the rockwork and even timid fish swim out in the open. It is truly a sight to behold and the primary reason why most hobbyists enjoy watching their fish, corals and inverts eat.

That is also why many of us are guilty of overfeeding at some point or another. Perhaps you feed too much, too often or both. We know you love to watch your babies eat, but if you want to reduce the nitrates in your tank, you are going to need to cut back (perhaps way back) on your feedings.

Frequent small feedings are better than occasional large ones. Using a fish food strainer to remove nitrate and/or phosphate-laden binders from frozen fish food prior to feeding can be helpful.

Frozen fish food is filled with nutrients, but the liquid juices these foods are packed in can sometimes leave behind undesirable pollutants. A fine mesh fish net is a tool you may already have handy that can hold frozen food while you rinse and thaw it with RO/DI water prior to feeding.

Dosing Red Sea NO3:PO4-X can gradually lower the nutrient levels in your tank.


There are liquid aquarium supplements designed specifically to reduce the nitrate levels in your aquarium. While these solutions are effective at lowering nitrate, they do not magically fix whatever is causing your nitrates to be high in the first place.

Liquid nitrate removers work in conjunction with your protein skimmer and/or other filtration equipment to enhance their ability to pull out nitrates or break them down.

One such supplement is AZ-NO3 Nitrate Eliminator. The manufacturer says AZ-NO3 "works entirely by aerobic cellular respiration on the target nitrate molecule, which is then removed by the protein skimmer."

Another option is Red Sea NO3:PO4-X Nitrate & Phosphate Reducer. Red Sea says their solution will "ensure steady bacterial propagation and complete nitrate reduction to nitrogen gas." They also state that efficient protein skimming is essential to provide the necessary oxygenation of the aquarium and to remove bacterial flocks from the water.

A third choice many of our staff has used to lower nitrate levels is Prodibio BioDigest. BioDigest is a hyper-concentrated bacterial compound sealed inside single-dose glass vials to preserve the efficacy of the ingredients. The recommended dosage is one vial per 50 gallons of aquarium water every 15 days.

BioDigest is made up of natural nitrifying, nitrate reducing and facultative bacterial strains selected for their ability to convert ammonia into nitrites, nitrites into nitrates and nitrates into nitrogen. These bacteria actually work together, with each strain finishing off the work started by the others. Some are capable of biosynthesizing nitrate-reducing enzymes in aerobic conditions. This enables water to be effectively purified, nitrates and phosphates to be reduced and prevents the spread of filamentous algae.

Biopellets run inside an upflow reactor can help lower nitrates and phosphates.


Biopellet filter media first hit the hobby about 6 years ago. Many reef aquarists have reported success using biopellets to reduce the nitrate and/or phosphate levels in their aquariums since.

Biopellets are beads or pellets of a solid plastic, used in an upflow reactor, for nutrient control. The basic idea behind this methodology is that a source of organic carbon, in this case pelletized biodegradable polymers in a fluidized reactor, is connected to the system (Murray Camp, 2012).

Marine heterotrophic bacteria—bacteria that must "uptake" carbon from sources in the surrounding water column—"feed" on the polymers, and in the process uptake other dissolved nutrients, such as nitrate and phosphate. For more information about biopellets, check out these articles by Murray Camp and Brad McCarty.

It takes a little time for bacteria to colonize on biopellets, but once established, they are very effective at keeping nitrate levels in check.

According to Reef Interests, makers of NP BioPellets and the recently released All-In-One BioPellets, the pellets "allow aerobic growth of bacteria which consequently consume nitrate and phosphate simultaneously."

Refugiums can be used to cultivate live food sources and for nutrient export.


I have always liked refugiums. I set up a refugium in all my aquarium systems, whenever possible.

Not only do refugiums reduce nitrate levels, they also help keep your pH stable (see diagram) and provide a safe haven for live foods (like copepods) to breed.

A refugium is a chamber within your aquarium system that is separate from your display tank. This chamber may be inside a sump, a separate aquarium, inside your tank, inside a back filtration chamber or hanging on the tank itself.

Within the refugium, you might add a deep sand bed with macro algae and/or live rock to help filter your aquarium water. Watch this video to learn more about the benefits of having a refugium and, when you're ready, read this article to help you set one up for yourself.

A nitrate reactor lowers nitrates without a skimmer regardless of phosphate levels.


Many hobbyists regard sulfur-based denitrate reactors as the ultimate solution for nitrate removal in a fish tank.

Joe from our staff recently called the Korallin Bio-Denitrator "just about the most hands-free and most-effective denitrifying filter available for your aquarium" (check out his review on this blog for the skinny). Another cool feature about the Bio-Denitrator is that it can be converted into a calcium reactor once your nitrates are under control.

By creating an anaerobic chamber inside the reactor, a colony of nitrate-consuming bacteria is established on the sulfur media. As long as the chamber is anaerobic, bacteria will grow and nitrate will be consumed. It is an extremely effective and proven method of lowering nitrates. Continual use in aquariums with high bioload (fish-only systems or reefs with a high fish population) will help keep nitrates at healthy levels. member Islandoftiki's Innovative Marine Micro Nuvo Aquarium.


Whether you keep it simple with water changes, take the "high-tech" approach or both, you owe it to your aquarium inhabitants to provide the healthiest environment possible.

If you have questions about nitrate control, aquarium equipment or reef tanks in general, please do not hesitate to contact us. We are here to help you succeed and will be there for you every step of the way.