Marine fish, corals and invertebrates are delicate specimens that require pristine water conditions to thrive. High nitrate is often the cause of algae problems and ailing fish or corals. In a fish-only aquarium, you will want to keep the nitrate level below 10ppm. In a reef aquarium, the nitrate level should be as close to zero as possible.

The first step in keeping your nitrates in check is to have an accurate test kit. Both Salifert and Red Sea make excellent nitrate kits. Make sure to test on a weekly basis so that you can correct any problems before the nitrate level is high enough to harm your tank inhabitants. Below are the various methods of lowering nitrates in your aquarium.

Water Changes

The most commonly practiced method of nitrate removal is through water changes. Water from the aquarium, high in nitrates, is removed and replaced with fresh salt water. 5%-10% water change every 1-2 weeks is ideal.



Protein Skimmers

As nitrates are constantly being produced in your aquarium, it can sometimes be very difficult to lower nitrates through water changes alone. An efficient protein skimmer will help greatly as it removes organics before they breaks down. The AquaMaxx Hang-On Skimmer is great for smaller aquariums up to 75 gallons. While the AquaMaxx In-Sump Protein Skimmers and Reef Octopus Aquarium Protein Skimmers models are great for larger tanks.



Bio-Pellet Reactors have become quite popular. It is an effective way of reducing and controlling your nitrate levels. Biopellets are made of biodegradable polymers. When used in a fluidized reactor, bacteria begin to feed on this polymer in conjunction with up-taking carbon sources (nitrates & phosphates) in the water column. A “biofilm”, composed of bacteria and assimilated nitrates and phosphates, develops on the Biopellets which then breaks off from the tumbling action. The fallen off biofilm is then exported via the protein skimmer or a mechanical filter. For tanks up to 150 gallons, the Hydra Aquatics BioPellet Reactor and the AquaMaxx BioMaxx BioPellet Reactor are excellent choices.


The Korallin BioDenitrator Nitrate Filter is also an excellent nitrate-reducing filter. Although it is more expensive, it is extremely low-maintenance and very effective at lowering nitrate levels through sulphur-denitrification (which is a process derived from commercial waste-water treatment plants). These Bio-Denitrators receives great reviews from our customers. Additionally, it helps to maintain your pH and can be converted to a calcium reactor should your needs change down the road.


Liquid Additives

Liquid additives can also be used to lower your nitrates, such as the AZ-NO3 Nitrate Eliminator 240mL and Red Sea NO3:PO4-X Nitrate & Phosphate Reducer - 500ml. They are more economical as no additional pieces of equipment are needed, but do take longer to work and require daily dosing and monitoring.



For a natural nitrate removal method, the addition of a refugium can be helpful. The CPR AquaFuge 2 Hang-on Refugium can be added to just about any aquarium. For larger aquariums, a sump-style refugium, such as the Precision Marine R24 Refugium w/ RL100 Protein Skimmer, would be a great choice. Simply fill the refugium with sand, rock rubble and macroalgae (typically chaetomorpha). Both the sand and liverock rubble will aid with denitrification, while the bulk of the nitrate reduction will be handled by the growth of the macroalgae. Proper lighting is required for the growth of the macroalgae. Another benefit of a refugium is that is also a place where micro-organisms (such as copepods and amphipods) can reproduce without being eating by your fish or corals. As they reproduce, a number of them will find their way in to your main tank to provide a natural and live food source for your tank inhabitants.

Many of the methods of lowering nitrates mentioned above can be use in conjunction with one another. If you have any questions or need help picking out the right equipment for your aquarium, please feel free to email us at or give us a call at 800-566-3474.