Can’t Lower Nitrates in Reef Tank? Here’s How to Reduce Them Safely

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You can’t lower the nitrates in your reef tank no matter what you do. On top of that, you have a problem with uncontrolled algae growth. If any of these problems feel familiar, you are not alone.

High nitrates in a saltwater aquarium have troubled many aquarists before you and will many after you. It’s part of the hobby, after all.

Maintaining the nitrates at the appropriate levels is one of the keys to a stable and thriving saltwater aquarium.

In this article, we will discuss the reasons that cause high nitrates in a reef tank, different ways to reduce them safely, and what are the ideal nitrate levels for your aquarium.

Let’s get started!


What are nitrates?

Nitrate is an ion that forms as an end product of the biological filtration and the nitrogen cycle. 

The fish waste and the food you introduce into your reef tank are broken down to ammonia (NH3) and then converted by the beneficial nitrifying bacteria to nitrite (NO2) and later nitrates (NO3).

Nitrates are not harmful to the tank inhabitants, at least when they are in acceptable ranges. 

On the other hand, ammonia and nitrites are particularly detrimental to the marine life in your reef tank and should be at undetectable levels.

High levels of nitrates are often associated with excessive growth of unwanted algae. Maintaining the nitrate levels stable will help you find balance and equilibrium in your reef tank.

What causes high nitrates in a reef tank?

The nitrate levels in the oceans are relatively low compared with the nitrates in our home aquariums. 

Corals need nitrates to grow, but not in high quantities. The excess nitrate levels will contribute to algae growth.

Lack of biological filtration, infrequent water changes, and overfeeding are often the main reasons for elevated nitrate levels in saltwater aquariums. 

In addition, inadequate mechanical filtration can raise the nitrates in your reef tank.

Acceptable nitrate levels in saltwater aquarium

The acceptable nitrate levels in a saltwater aquarium should be in the 0.1 to 5 ppm range. However, it’s not that simple, and there are a lot of variables. Let me explain.

The right nitrate level in your reef tank will depend on the corals you want to keep. 

Mixed reef systems will tolerate nitrate levels at 20, 30, and even 40 ppm, but it doesn’t mean they’ll thrive. SPS corals, however, prefer ultra-low nutrient systems with nitrate levels lower than 1 ppm.

These numbers are just a general rule of thumb. Most people keep their tanks between 1 to 10 ppm and have thriving tanks.

Keep your nitrates under control at the desired level, and you should not have a problem.

New saltwater tank high nitrates

It’s perfectly normal to have high nitrates in a new saltwater tank. During the nitrogen cycle, the nitrifying bacteria convert the ammonia to nitrite and later to nitrates.

When the cycling period finishes, you should make a large water change to reduce the nitrates to a minimum.

Remember, you should not measure the nitrates until the nitrites levels reach zero. If you have detectable levels of nitrites in your reef tank, you will get false nitrate readings.

How to reduce nitrates in a saltwater aquarium?

There are many ways to lower the nitrates in a reef tank. Some are easy as a water change; others require investing in an adequate filtration system. 

Here are the most popular methods for lowering nitrates in a reef tank.

Do a water change

When it comes to reef tanks, regular water changes are the best way to manage nitrates and, at the same time, replenish all the depleted micro and macro elements in your water.

However, water changes will decrease the nitrate level in your tank but will not eliminate the source. 

You can’t rely on water changes unless your tank is light on stock or you do large water changes as much as 50 percent weekly.

Invest in a quality RO/DI System

Unless your tap water is near 0 TDS ( highly unlikely), you will need RO/DI system. A reverse osmosis system is a piece of must-have equipment in every serious reefer arsenal.

The RO/DI system will remove nitrates from your tap water and other undesirable elements.

Don’t overstock your tank

Many beginners add more organisms than they should, and sooner than later, they face many problems. Every fish you add to the system contribute to the overall nitrate numbers.

Don’t go overboard with the number of fish you keep unless you have quality nitrate export.

Feed less fish food

We all love to feed our fish, but sometimes less is more. 

It’s better to feed your fish in small quantities several times a day than give them a large feeding at once.

The uneaten food will decompose and increase the nitrate levels in your reef tank.

Use a protein skimmer

The protein skimmer is valuable equipment that removes the excess organic matter from your reef tank. The protein skimmer removes the excess waste before it breaks into ammonia, nitrite, and nitrate.

Build a refugium

Refugiums are highly effective in reducing the nitrate levels in a saltwater aquarium. 

Refugium is a small compartment in your sump filled with macroalgae and live rock. 

The macroalgae use nitrogen to grow, acting as nutrient export for your main display tank. It is an excellent way to control the nitrate levels in your reef tank.

There are other methods to lower the nitrates in your reef tanks such as using a deep sand bed, carbon dosing, and sulfur denitrator. 

However, the methods mentioned earlier in this article are more than enough to manage the nitrate levels and build a thriving reef tank.

Final Thoughts

As you have seen above, there are many ways to manage the nitrate levels in your reef tank. 

I keep a nano reef tank without a skimmer, so the most convenient way is to do regular water changes. Everyone has their preferences to decrease the nitrates in their reef tanks. Whatever works for me, it might not work for you.

Now I would like to know. What is your preferred way to reduce the nitrate levels in your tank? 

Let me know in the comment section below!

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