Nitrates are not all bad, in fact, our tanks need some level of nitrates in order to survive. It's only when nitrates become elevated beyond acceptable levels do we start to see a problem. Elevated nitrates in a reef tank reduce water quality, interfere with coral health, and contribute to nuisance algae growth. The key is keeping your nitrates at low levels without starving the tank completely of vital nutrients. 

Why Are Nitrates Important in Reef Tanks?

Nitrates are vital to your tank's health and are created as the end by-product of the nitrogen cycle. All of the organic material that breaks down in your tank including fish waste, food, and even dead algae eventually releases some level of nitrate. The more organic material you put into your tank, the more nitrates you get.

Since an aquarium is an enclosed ecosystem and fish and other animals have to eat, you can't exactly stop feeding your tank as a means of limiting nitrate. As hobbyists, we must rely upon filtration and maintenance to export the nitrates as they build up in our aquariums. If your methods of exporting nitrates are not sufficient enough to keep up with your food input, nitrates start to stack up.

An acceptable nitrate level in a reef tank is 3 - 5 PPM. Keep in mind that some hobbyists can succeed with higher levels of nitrates but this is the exception. For most of us, a target of 3-5 ppm produces the best results. 

Water Testing

How to Prevent Nitrate Spikes

An abrupt rise in nitrate is called a "nitrate spike" which can be caused by overfeeding, dead livestock, or even stirring up all the collected detritus in your substrates. Most importantly, you need to test your nitrates in order to identify a trend of rising nitrates. If you're not testing, you won't ID the problem until after it's too late.

  • New aquariums: Test nitrates every 3-4 days to monitor the cycle.
  • Upon introducing new livestock: Test every 3-4 days until you're confident that nitrates are not rising.
  • Established aquariums: Test every 1-2 weeks. 

Algae on gracilaria

How to Remove Nitrates From a Reef Tank

There are multiple ways that hobbyists commonly export nitrates from an aquarium. In most cases, you won't have to use all the methods, only what is required to maintain acceptable levels of nitrate.

1. Reduce Feeding

Overfeeding really is the most common cause of a nitrate spike. While it's important to ensure your fish's nutritional needs are taken care of, feeding in a hurry or simply adding too much food is easy to do, even for experienced hobbyists.

  • Always turn off your pumps and filtration; this prevents food waste.
  • Feed slowly, and watch your fish consume every morsel of food. Add a little, watch them eat, then add a little more.
  • Use feeding rings to contain food on the surface.
  • Use a squirt feeder to deliver food where it's needed.  
  • Monitor your automatic feeder closely or just turn it off altogether.
  • Be conservative with coral foods.

Reef Tank

2. Change Your Type Of Food

Some fish foods are much more nutrient dense than others. Pellet food is the worst culprit in terms of creating nitrates because it is the most nutrient-rich type of food. If you are exclusively feeding pellet food (or flakes), switch it up and add frozen food into the mix.  Maybe just feed frozen food 1-3 per week or once per day, then fill in the gaps with your primary dry pellet food. Avoid lower-quality fish foods that contain fillers or unnatural ingredients like wheat and corn. 

3. Increase or Maintain Mechanical Filtration

Mechanical filters remove suspended particulate waste before it is broken down into nitrates. Always change your filter socks every 1-3 days and never let them clog up completely. Clean your protein skimmer as often as possible to ensure optimal performance. Consider using an automatic filter roller or even a BRS Reactor with a sediment filter inside as means of turbocharging your mechanical filtration. 

Filter Sock

4. Refugiums, Macroalgae Reactors, and Turf Scrubbers

If you are not already using some means of natural nitrate reduction, consider a refugium with macroalgae, a chaeto-reactor, or turf scrubber. These methods are very popular because they are effective and there is no ongoing maintenance cost after you get one set up.

While each of the various algal filtrations is set up differently, all of them rely upon the same concept of using algae growth as a means of removing nitrate. As algae grow, it will take up nitrates (and phosphates) from the aquarium water and then all you have to do is harvest the algae to effectively export nitrates from your aquarium. 

5. Carbon Dosing & Biopellets

If all else fails and you just cannot get nitrates under control, you can start to research carbon dosing or the use of biopellets. These methods are much more advanced and should be reserved for only the most advanced aquarists who understand when and where these techniques should be applied. 

While both carbon dosing and biopellets are very effective means of nitrate removal, then can be dangerous in that you run the risk of starving your tank of vital nutrients. These methods effect the bacterial balance in your aquarium and can lead to instability if not maintained correctly.  

Do Water Changes Work To Reduce Nitrates?

While removing water from your aquarium does remove a portion of your tank's nitrate levels, the actual reducing effect is minimal. A 10% water change only removes 10% of your current nitrates. You would have to be changing upwards of 50% or more of your aquarium's water to make an impact on elevated nitrates.

Repeating small 10-20% water changes every other day until you have effectively changed out a much larger percentage of the water is an alternative approach, but in terms of regular maintenance, a typical weekly water change is not all that effective at reducing nitrates. The rate we introduce nitrates as food for the fish and corals simply exceeds the rate at which we can export them via water changes.