All You Need to Know About: Nitrate

All You Need to Know About: Nitrate

Most novice hobbyists think of nitrate as bad, and in higher amounts, it’s certainly not good for reef tanks. However, corals still require a small amount of nitrate for optimal color, growth and health.

What is Nitrate?

Nitrate is a naturally occurring compound that forms when nitrogen combines with oxygen. In an aquarium, nitrate is predominantly the by-product of fish and other waste. As this waste breaks down, it is converted from ammonia as part of the nitrogen cycle.

Why is Nitrate Important?

Nitrate is an essential food source for the zooxanthellae found in the surface tissues of coral polyps. In exchange for a protected environment, these zooxanthellae provide the coral with nutrients they need to survive and grow. Proper levels of nitrate may also help improve coral colors. However, if nitrates become too high, they can stunt coral growth, cause corals to turn brown and cause nuisance algae. High amounts can also cause fish illness and even death.

What is the Optimal Range?

Reef Aquariums: 0.025 ppm- 5ppm

Tools for Measuring Nitrate

Here are the most common options for measuring nitrate in a reef tank, priced high to low:


The most expensive option, a photometer, is both accurate and easy to use. Place a water sample in a small testing chamber and the photometer will display results on a digital readout.

Hand-held Tester

A hand-held tester, also known as a colorimeter, is also easy to use. Compared to a photometer, it is relatively inexpensive. Similar to a photometer, place a small water sample in a chamber for analysis.

Test Kit

A test kit is a commonly used method for measuring nitrate and are relatively inexpensive. These will test a sample of water, which is then color-matched on a chart to determine the current amount.

How To Maintain Nitrate Levels

Here are the most common ways to maintain nitrate levels:

1. Regular Water Changes

Regular water changes remove a percentage of the water and replace it with clean nitrate-free water, reducing nitrate levels. If amounts are too high, more frequent water changes are recommended until these levels return to the optimal range.

2. Do Not Overstock

If your tank is overstocked, more fish will lead to more waste and an increased amount of nitrates.

3. Do Not Overfeed

By overfeeding, fish will produce more waste. As a result, any uneaten food will decay and result in higher nitrates.

4. Dose Carbon

An organic carbon source, usually in the form of a liquid, provides food for good bacteria in the system. As these bacteria multiply and grow, they consume nitrates and phosphates from the water. An efficient protein skimmer removes excess bacteria from the water column. Bio-pellets are another form of carbon dosing and works similarly to liquid carbon dosing.

5. Add a Refugium

Adding a refugium with macroalgae will naturally reduce nitrates as the macroalgae consume the nutrients. Ensure the refugium is large enough for the total volume of water in the tank.

What is the Relationship Between Nitrate and Phosphate?

In nature, nitrates and phosphates are consumed by corals in a 16:1 ratio known as the Redfield Ratio. If there is not enough nitrate, then the good bacteria in the system can’t effectively consume phosphate, causing phosphate to rise. In turn, high phosphate levels generally lead to the proliferation of nuisance algae. The opposite is also true; if there is not enough phosphate, the good bacteria cannot effectively consume nitrate.

Learn More About the Redfield Ratio:

And there it is! Nitrates play an essential part in our reef tanks, and it is best not to let them get too low or too high. Regular testing and water changes are critical to preventing a potential issue with nitrates.

We hope you learned something today about nitrates.  If you are looking for additional information regarding other compounds and topics, please visit our weekly Simplicity Aquatics blogs for more details.

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