Posted on

Aquarium Basics 101 – Nitrogen Cycle, What is it?

The nitrogen cycle is a process that occurs in all aquariums, and it is essential for maintaining the health of the fish and other organisms living in the aquarium. This document will explain the “Cycle” and how it works.

Fig.A1 – Full Nitrogen Cycle

NH3 (ammonia) to N02 (Nitrite)

The nitrogen cycle begins when fish produce waste in the form of ammonia. Ammonia is toxic to fish and must be removed from the water. Bacteria called nitrosomonas (Fig.A2) convert the ammonia (Figure A.2 – Steps 1 to 2) into nitrite, which is also toxic to fish.

Nictrosomonas Fig .A2

The nitrogen cycle is important because it helps to break down the harmful waste produced by the fish and other organisms in the aquarium, making it safer for them to live in. It is essential to establish the nitrogen cycle in a new aquarium before adding fish to it, as the fish will produce waste from the moment they are introduced to the aquarium. This can be done through a process called “cycling” the aquarium, which involves adding a small amount of fish or using a product called a “cycle starter” to provide a source of ammonia. There are many different companies that make these cycle starter products. The bacteria that convert the ammonia and nitrite will then grow and establish a colony, allowing the nitrogen cycle to begin.

N02 (Nitrite) to N03 (Nitrate)

After nitrite is produced in an aquarium, it is then converted into nitrate by a type of bacteria called nitrobacter. (Fig.A3) Nitrite is toxic to fish and must be removed from the water to maintain the health of the fish and other aquatic life in the aquarium. Nitrobacter bacteria are found in most healthy aquariums and play an essential role in the nitrogen cycle by converting the toxic nitrite into the less toxic nitrate.

Once the nitrite is converted into nitrate (Fig.A1 – Steps 3 to 4), it can then be removed from the water through regular water changes. Nitrate levels that are too high can also be harmful to fish and other aquatic life, so it is important to monitor nitrate levels and perform regular water changes to keep them at a safe level. In a healthy aquarium, the nitrogen cycle will continue to process the fish waste, maintaining a balance between ammonia, nitrite, and nitrate and helping to keep the water clean and safe for the fish and other aquatic life.

Nitrobacter FigA.3 – Another type of bacteria called nitrobacter convert the nitrite into nitrate, which is less toxic to fish and can be removed through regular water changes.

How to remove Nitrate (N03) from your system.

There are a few different methods that can be used to remove nitrate from a marine aquarium, including:

  1. Water changes: Regularly performing water changes can help to reduce the nitrate levels in your aquarium. By replacing some of the water in your tank with fresh, clean water, you can dilute the nitrate concentration.
  2. Nitrate-removing media: There are several types of nitrate-removing media available for use in aquarium filtration systems, such as denitrifying filters or nitrate-removing resins. These can be effective at removing nitrate from the water.
  3. Live rock and macroalgae: Live rock and macroalgae can be used to naturally remove nitrate from the water. These organisms are able to take up nitrate and use it as a source of food, reducing the nitrate levels in the water.
  4. Nitrate-reducing bacteria: Certain types of bacteria can be used to convert nitrate into nitrogen gas, which can then be released into the air. This is known as denitrification and it can be done in a denitrification filter, also called a deep sandbed, can be added to the filter system.
  5. Algae turf scrubbers : this device uses algae to absorb nitrate in the water and it is a natural, efficient and low maintenance way to remove nitrate.
  6. Macro Algaes : using different macro algae in a refugium is also a very effective way to remove Nitrates. This does require removing or cultivating the algae as it grows, as to not allow the nitrates to be reintroduced into the aquarium.

It’s important to note that it’s not always necessary to completely eliminate nitrate from your marine aquarium, as some nitrate is required for the growth of beneficial microorganisms in the tank. Typically, a nitrate level of 20-40 ppm is considered acceptable in a marine aquarium.

It is also important to address the cause of high nitrate level, to prevent it from happening again, overfeeding, overstocking, lack of maintenance etc.

Water Changes – The most effective way to remove N03 (Nitrates) (Fig.A1 – Steps 5)

Water changes are a simple and effective way to remove nitrate from a marine aquarium. The basic idea is to replace some of the water in the tank with fresh, clean water. This dilutes the concentration of nitrate in the tank and can help to reduce nitrate levels over time.

To perform a water change, you will need to have a separate container of clean, pre-mixed saltwater that matches the temperature, salinity, and pH of your tank. It is recommended to use a good quality water conditioner to remove chlorine and chloramines from tap water, if you use tap water as a source.

Here are the general steps to perform a water change:

  1. Turn off any equipment, such as pumps or filters, that may disturb the water or the inhabitants of the tank during the water change.
  2. Use a clean and dedicated siphon or pump to remove some of the water from the tank, typically about 10-20% of the total volume depending on the nitrate level and the size of your tank, it could be more or less.
  3. Add the pre-mixed clean water to the tank, to replace the water that you removed.
  4. Keep an eye on temperature and salinity level, use a hydrometer or refractometer to make sure the new water matches the tank’s water.
  5. Once the water change is complete, turn the equipment back on and observe the tank for a few minutes to make sure everything is running smoothly.

It’s important to do water change regularly and consistently. A good schedule can be once a week or every other week, depending on the size of the tank and the bioload it has. Keep in mind that more frequent water changes will be necessary in tanks with high nitrate levels, or if there are a lot of fish or other inhabitants in the tank.

Also it’s important to use a good water test kit, to keep an eye on the nitrate level before and after each water change, this will help you determine if the changes you are making are effective and if more is needed to be done.

Macro Algae – Refugium – Another effective way to remove N03

There are several types of macroalgae that can be used to remove nitrate from marine aquariums. Some of the most commonly used types include:

  1. Caulerpa: This type of macroalgae is available in several different varieties and can grow quickly in a variety of lighting conditions. It is also able to take up nitrate and other nutrients from the water, making it an effective choice for removing nitrate from a marine aquarium.
  2. Chaetomorpha: Also known as “spaghetti algae,” chaetomorpha is a type of green macroalgae that is known for its ability to remove nitrate, phosphates, and other nutrients from the water. This algae is a very good option if you are looking to address high levels of nitrate as well as other issues like phosphates.
  3. Red Macroalgae: Such as Gracilaria and Hemprichii, These macroalgae species are also known for their ability to absorb nitrate from the water and are also a good alternative for those looking for a more decorative option for their aquarium.
  4. Halimeda: This is a genus of calcareous green macroalgae, it is slow-growing but effective in removing nitrates from the water and can also help to maintain proper pH levels in the aquarium.

It’s important to note that some of these macroalgae can be invasive, and if they grow too much or get out of control, they can actually contribute to nitrate problem, but this can be controlled by pruning and keep a healthy balance between the algae and the other inhabitants of the tank.

It is also important to have a proper lighting and flow to support the growth of these macroalgae, and to make sure that you don’t have any herbivorous fish or invertebrates in the tank that will eat them.