How to Lower Nitrates in a Fish Tank

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    Alina Andreeva

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  • Updated on: 17/04/2020

Most fish keepers know all about the dangers of ammonia and nitrite within their tanks, however, the impact of nitrate is often less understood. Nitrate is not as lethal as either ammonia or nitrite, but it can still have a negative effect on your fish over time. Therefore, it is important to know the dangers of nitrate and how to regulate the levels within your aquarium, for the good of your pets and the overall environment of the tank.

how to lower nitrates in a fish tank@David Clode

What causes nitrate in a fish tank?

Nitrate can build up within a fish tank through a number of different ways. As a by-product of nitrite oxidation, some levels of nitrate can be found within the vast majority of tanks, no matter how careful you are. Decaying plant material can result in increased nitrate levels, as can detritus, and dirty filters. Not only this, but overfeeding your fish can also raise the nitrate levels within the tank, as well as overstocking your aquarium with too many plants and fish for the space in question. Many people choose to fill their fish tanks with tap water when it comes to cleaning time, however, this can also add to the nitrate levels already within the aquarium. Some drinking tap water, despite being safe for human consumption, can contain 40 parts per million of nitrate. This may not sound like much, but you should be aiming for a water source with around 10 parts per million or below. Nitrate-free water sources are ideal when it comes to filling your tank.

What nitrate level is safe for fish?

In the wild, water nitrate levels within fish habitats are often extremely low, around the five parts per million mark. Therefore, if you are aiming to replicate the correct natural conditions, you should be looking to reduce your nitrate levels as much as possible. If you are keeping a freshwater aquarium, the nitrate levels should never go above 50 parts per million, or else you risk causing significant damage to the fish within. Preferably, your nitrate levels should always be below the 25 parts per million mark, but the lower the better. If you are looking to breed fish, or want to reduce the amount of algae growing within your tank, aim for a nitrate level of below 10 parts per million.

What effect does nitrate have on fish?

nitrates in a fish tank@pookpiik / Freepik

Fish will often begin to feel the effects of high nitrate levels once they reach between 50 and 100 parts per million. If left in conditions of this nature for a sustained period of time, the fish will start to develop health problems. Their immune systems will be weakened, making them more susceptible to disease and illness. Not only this, but their ability to reproduce will be inhibited by the high levels of nitrate. When it comes to young and fry fish, high nitrate levels can also affect their ability to grow. It is also important to know that many of the conditions that cause nitrate also cause a decreased level of oxygen within the water, heaping more stress upon your pets.

What effect does nitrate have on algae?

The short story is the higher your nitrate levels, the higher your chances of algae growth. The growth of undesirable algae is promoted at nitrate levels as low as 10 parts per million. As you rise above these levels, the growth of algae only increases further. Not only this, but if your nitrate levels are rising faster than your normal plants can use them, they will likely be overtaken by algae, before eventually dying.

nitrates in a fish tanks@kaikoro / Freepik

How do you lower nitrates in an aquarium?

Now that you know the dangers of high nitrate levels within your tank, it is time to learn exactly how to lower them and keep them low. It is important to know that well-oxygenated filters will not allow nitrate-removing bacteria to thrive, as these bacteria avoid high oxygen environments.

  • Clean your tank regularly. The first and simplest step to reduce nitrate levels is to keep your tank clean. Waste produces nitrate, therefore, a clean tank is your best friend.
  • Feeding. As we mentioned before, overfeeding can actually cause a rise in nitrate levels, as well as other waste. Again, this is a simple fix. Only feed your fish the designated amount. Look on the back of the food packet/container for more information. If you notice that food is regularly being left by the fish, then reduce by a little each day until you reach the perfect amount.
  • Plants. Keeping live and healthy plants within your tank can reduce nitrate levels, as these plants use nitrate to survive. Just be careful that your nitrate levels stay at a reasonable level, otherwise these plants can be overgrown by algae.
  • Water changes. Changing the water within your tank should be a regular part of your schedule anyway. However, it is also important to ensure that the water you are using is either low in nitrate or nitrate-free. If you have tested your tap water and found that it is high in nitrate, then opt for deionised water or reverse osmosis water instead. However, mineral substitutes may be needed with these water types.
  • Equipment. If you have the money to invest in a filter that removes nitrate, then do so. If not, you can purchase a nitrate-lowering media to help your existing filter achieve the same goal.

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