How to lower nitrates in a fish tank

How to Lower Nitrates in a Fish Tank?

One of the biggest challenges in maintaining an aquarium is preventing nuisance algae growth. Despite their ability to generate energy from light through photosynthesis, algae require nutrients in their surrounding environment to grow and thrive. They cannot simply appear out of nowhere. These nutrients primarily comprise ammonia/ammonium, nitrite, and nitrate, the preferred form for most plants. Controlling the number of nutrients in the water will prevent algae growth. It can be done by keeping the levels of macronutrients, like nitrate, at a low concentration. Overfeeding fish, neglecting water changes, and failing to replace chemical filters can all contribute to an excess of nutrients, leading to unwanted algae growth. Therefore, maintaining a healthy balance of nutrients in the aquarium is essential to keep algae under control.

How to lower nitrates in a fish tank?

The following are the methods to reduce the nitrates in a fish tank:

Minimize nitrate input

It is an effective way to minimize nitrate input and lower nitrates in the tank. Overfeeding your fish can lead to excess nutrients, including nitrate, so try to feed them only what they can consume in a few minutes and remove any uneaten food. Regular cleaning and water changes can also help remove excess nutrients, including nitrate. Adding live plants can help absorb excess nutrients and convert them into biomass as part of their growth.

In contrast, an efficient filtration system can help remove organic waste and other particles from the water, reducing the number of nutrients available for algae growth. Finally, adding too many fish at once can lead to a buildup of waste and excess nutrients, including nitrate, so it’s important to add fish gradually to allow the biological filtration system to adjust to the new load.

Conducting water changes

Regular water changes are crucial to maintaining a healthy and balanced environment in a fish tank with lower nitrates. The first step is to test the water to determine the current nitrate level. Even if the levels are low, regular water changes are important to remove impurities or toxins. The volume of water you change will depend on the size of your aquarium, but a general rule of thumb is to change about 10-20% of the water every 1-2 weeks. When preparing the water for the change, ensure it is at the appropriate temperature and pH level to match the water in the aquarium. Consider using a water conditioner to remove any chlorine or chloramine in tap water. Use a siphon or a gravel vacuum to avoid disturbing the substrate too much, which could release excess nutrients and increase nitrate levels.

Install a Refugium

For those not keen on performing regular water changes in their fish tanks, an alternative method can greatly reduce the need for such a task. Using a planted refugium, the aquarium keeper can facilitate the direct uptake of nitrate from the water by using living macroalgae. This process involves the removal of nitrate and other nutrients from the water when portions of the macroalgae are harvested and removed. Although it may require additional investment to set up, using a refugium offers significant long-term benefits in continuous, effortless, and natural nitrate removal. Cultivating the macroalgae can be quite an enjoyable and rewarding effort in and of itself, as some varieties can be very aesthetically pleasing.

Use Microbes

Biological action can control nitrate levels in fish tanks by using various microbes. These microorganisms can cause either sequester nitrate to produce biomass or convert it to another substance, such as nitrogen gas. The market now offers live cultures of both aerobic and anaerobic microbes. Aerobic bacteria can quickly take up nitrate but require a carbon source like ethanol to feed on.

Unlike aerobic bacteria, anaerobes don’t pose the risk of blooms caused by carbon overdosing, which can lead to dangerous oxygen depletion. On the other hand, anaerobic bacteria like purple nonsulfur bacteria work more slowly but do not require carbon dosing since they can be found in the bottom sediments with ample organic matter. It’s best to have a diverse microbial community in the tank, which can be fostered through deep sand beds, bacterial inoculants, and the regular addition of bacterial supplements or foods. A strict water change routine, purified water, quality chemical filters, refugium installation, and beneficial microbial growth support can manage nitrate and keep a healthy, relatively algae-free fish tank.

Role of fish tank nitrate

In natural environments, nitrate is a critical nutrient that can deplete quickly due to its importance for the growth and reproduction of plants. However, nitrate accumulates in fish tanks due to the recirculating system that filters and recycles water. For instance, the nitrogen cycle that converts ammonia to nitrate can result in nitrate accumulation if not managed properly. Therefore, it is crucial to test the nitrate levels in the aquarium water regularly using a quality test kit like the API Nitrate fresh and Saltwater aquarium test kit. Nitrate levels above 10 or 15 parts per million (ppm) indicate the need to take action to prevent nitrate buildup.

Frequently asked questions:

What is the fastest way to lower nitrates in an aquarium?

A: Performing a water change is the quickest and most direct way to lower nitrates in an aquarium. It involves replacing some of the tank water with fresh, clean water. The amount of water changed will depend on the current nitrate levels and the size of the tank, but typically a 25-50% water change is recommended.

What causes high nitrate levels in a fish tank?

A: High nitrate levels in a fish tank are usually caused by excess fish waste, uneaten fish food, decaying plant matter, and insufficient water changes.

How can I test if my fish tank has high nitrate levels?

You can easily test nitrate levels using a water testing kit designed for aquariums. Simply follow the instructions provided to obtain accurate results.

Are nitrate removers safe for fish and aquatic life?

Nitrate removers are generally safe for fish and other aquatic life when used as directed. Just make sure to carefully follow the product instructions and keep an eye on your water parameters.

How often should I clean my aquarium filter?

The frequency of cleaning your aquarium filter depends on the filter type and your tank’s specific needs. As a general guideline, cleaning or replacing the filter media every four to six weeks will help maintain optimal performance.


Implementing a combination of measures is the best approach to lower nitrate levels. These include performing regular water changes, using high-quality chemical filtration, reducing feeding, avoiding overstocking, and adding live plants or a refugium. Using these methods, you can maintain a clean and healthy environment for your fish and other aquatic inhabitants. Moreover, fostering a diverse and healthy microbial community can also help to reduce nitrate levels in the aquarium. Regular monitoring of nitrate levels and water quality is also essential to ensure the long-term success of the aquarium.

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