How to Reduce Nitrate in an Aquarium

Although nitrate is not as lethal as ammonia or nitrite, high nitrate levels will eventually hurt the fish aquarium ecosystem in general.

Where Does Nitrate in Aquariums Come From?

The nitrogen cycle produces nitrate from nitrite oxidation. To some extent, it is present in all aquariums.

Decaying plant materials, dirty filters, overfeeding, overcrowding the aquarium, and detritus play a role in increasing nitrate levels.

Before you add water to your aquarium, give it a nitrate test to determine if the levels are within the recommended threshold. Nitrate levels that are over 10 ppm (parts per million) are not safe. So consider other nitrate-free water sources. Incidentally, tap water may contain nitrate, as is proven in cases like America, where drinking water can have levels up to 40 ppm.

What are The Correct Levels

Naturally, nitrate levels are very low in the water. In freshwater fish tanks, nitrate levels should be maintained at lower that 50 ppm at any given time. Below 25 ppm is even better. If you face challenges with algae infestation, the nitrate levels should go way lower than 10 ppm.

Effect of Nitrates on Fish

If the levels get to 100 ppm the fish will feel the effect. The result is stressed fish that are more prone to disease and cannot reproduce.

The growth of young fish is negatively affected by high nitrate levels. Decreased oxygen levels are caused by the similar conditions that result in elevated nitrate, which further puts fish under stress.

When the levels increase to levels the fish cannot accommodate, they become slow and may have blotched skin and open sores and might eventually suffer sudden death.

When a new fish enters an aquarium containing fish accustomed to high nitrate levels, they quickly die from shock.

The Relationship Between Nitrate and Algae

Increased nitrate significantly contributes to algae growth, and algae infestation will spiral out of control supported by nitrate levels of 10 ppm. Newly tanks experience algae blooms courtesy of the high nitrate levels.

When nitrate levels rise more rapidly than plants can utilize it, then the plants are at the risk of suffering asphyxiation and eventually death, because the algae can take over all space including growing on plants and suffocating them.

Ways to Reduce Nitrate Levels

There are two ways in which the nitrate levels can be lowered

  1. Minimizing nitrate input
  2. Promoting its uptake or removal
  1. Minimize the input of nitrates

Replacement water, supplements, and fish food are some of the sources through which nitrate finds its way into our aquariums. Conducting water change is the best way to minimize nitrates in the aquarium.

Large, regular water exchange effectively and permanently removes nitrate from the system. The amount of water exchanged is directly proportional to the nitrate removed. The math is simple. If you do a 20 percent water change, you will have removed 20 percent nitrate.

Frequent water changes featuring water that has low levels or no nitrate at all will bring down the nitrate levels. If your standard tap water or borehole water has elevated nitrate levels, the reverse osmosis water (RO) or deionized water (DI) can keep the levels down when used in the water change. However, this water is free of minerals. It is advisable to combine the nitrate-containing regular tap water with RO or DI water to attain the right mix with the desired balance.

Also consider doing the following to keep the nitrate levels low

  • Keep the aquarium clean 

Waste in the aquarium eventually leads to the production of nitrates. Clean your tanks to inhibit the production of nitrate, making it easier for the little levels to be removed by water changes.

  • Feeding 

Food leftovers and other undesirable waste are a significant contributor to excess nitrate. Feed the fish just enough to avoid piling leftovers at the bottom of the aquarium and reduce fish waste due to overfeeding.

  • Live plants 

Live plants use up nitrate and help keep the levels down. Plants use up nitrates as nutrients and food. Persistently, high nitrate levels usually result in an algae outbreak. It is advisable to add live plants to the aquarium to lower nitrate levels.

  • Overcrowding 

Keep the number of fish low in your aquarium. Alternatively, consider a bigger aquarium. Nitrate levels spike as a result of fish waste. Keeping the fish population low helps to prevent the accumulation of nitrate.

If continuous feeding still leaves you with high nitrate levels, you probably have too many fish for your aquarium set up.

  1. Promote nitrate removal or uptake

To avoid high nitrate levels, regular maintenance, and changing the water is the panacea. You have to ensure their levels are regulated by removing or absorbing the nitrate safely. Ignoring this mean that nitrate levels will rise, and your fish are likely to die. The following will remove or increase the uptake of nitrates

  • Daily Maintenance

Make sure fish finish their food by feeding them lightly in even less than two minutes. Feed them small amounts of food two or three times a day instead of one large helping once a day.

Avoid overcrowding the aquarium and only keep manageable numbers. Do a quick inspection every day and remove any decomposing material like dying plant leaves and stems, dead fish or neglected food items.

  • Weekly Maintenance 

Schedule frequent water changes at least weekly at minimum. They should be at least 50 percent or more to be considered sufficient at keeping water diluted. Ensure your tank is filled with nitrate-free water every time you perform a water change. That will help to avoid spiking the nitrate levels by using water with high concentrations of nitrate.

Regularly check the filters and change the replaceable parts of the filter medium as required at every cleaning. A plugged and seriously matted medium can be cleaned in a bucket or basin of tank water to remove the sludge and most decomposing material without ruining the bio-filter. The more the flow of oxygen-rich water through the media, the better its biofiltration capacity.

  • Plant Filtration

Low nitrate levels in an aquarium are naturally achievable by having a well planted tank. Plants put ammonia, nitrate and nitrite in the aquarium to good use. Always remember that plants only use up a certain portion of waste, and stocking the aquarium lightly is the solution.


It takes effort and a lot of work to maintain minimum levels of nitrate in an aquarium. However, the reward for your painstaking work is to watch your beautiful, healthy fish swimming in the comfort of your house. That far outweighs the work that goes into it.