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Fast Ways to Reduce Nitrates in Fish Tanks

So, you think there is a high nitrate accumulation in your aquarium? If so, it is important to get nitrates down to a manageable level to avoid harming your fish.

This guide explains several quick ways to lower the nitrate levels in water with expert tips for maintaining sufficient biological filtration.

A Brief Reminder about the 'Nitrogen Cycle'

In a healthy, contained system (e.g. fishbowl, fish pond) the aquarium nitrogen cycle is a continuous process that converts:

In other words, you need a good supply of beneficial bacteria and live plants to consume the waste products inside the tank.

When you first start a fish keeping hobby, it's easy for beginners to get confused about the toxicity of nitrite and nitrate. Think of it like this. Even low amounts of nitrite will be very toxic for your fish. But, nitrates are less so, and they take longer to build up.

For example:

One (1) part per million (ppm) of nitrite is enough to poison and kill most fish species kept in aquariums. Whereas, it's not uncommon for fish to survive one hundred (100 ppm) nitrate water levels.

Pro Tip: Mains water may contain some nitrates. So, you may be creating "Old Tank Syndrome" when you replace the old tank water with fresh water from the tap.

Simple Methods for Lowering Nitrate a Fish Tank

Changing at least 25% of the aquarium water is the quickest and easiest way to reduce nitrates. But, you need to make sure the source (e.g. tap water) has less NO3 than the water stored inside the fish tank. In other words, you should test them both before and after.


In most cases, it's not harmful to conduct water changes of up to 50% without creating any major issues. But, the replacement water needs to be the correct temperature, and treated for chlorine or chloramine (e.g. dechlorinated to remove chemical compounds that contain ammonia).

What if the domestic water is showing high levels of nitrate (over 40 ppm)? If so, some experienced aquarists use Reverse Osmosis (RO) instead. This simple process can remove nitrates, chlorine, phosphates, and other harmful minerals from faucet water.

1. Aquarium Plants Reduce Nitrates

Nature has already created filters that are able to "absorb" nitrates and use them for fertiliser. These simple nitrate filters are living plants.

Thus, the use of fast growing foliage will help you tackle a nitrate-laden fish tank. In fact, the best aquarium plants only need a few days to remove all toxic nitrates from a small tank.

In a nutshell, it's best to add some living aquatic plants as part of any aquascaping projects. Not only do they help you cycle the tank, they can also fight off algae and provide safety and shelter for small fish, scattered eggs, and fry.

Pro Tip: Remember, a planted aquarium needs the correct amount of lighting and fertilisers. Otherwise, you could struggle to keep your plants growing and healthy.

2. Liquid Nitrate Remover

Another method of getting the nitrate level lowered is by using a special liquid remover. For example, "Tetra Nitrate Minus" helps to reduce and control the levels of nitrate in an aquarium.

Plus, "Tetra Easy Balance" can help you stabilise water values for up to six (6) months. This is useful for extending the next water change (e.g. if you can't carry out regular maintenance yourself). But, remember to use them both as directed by the manufacturer.

3. Filter Media for Nitrate Reduction

Even though some bacteria are aerobic (they consume oxygen), anaerobic bacteria are good for reducing nitrate.

It is unlikely to be the quickest fix, but using the anaerobic population of bacteria in filter media (e.g. Seachem De Nitrate) will help.

4. Nitrate Removal Sponge

Some cheap filter sponges or foam, such as Nitrax Nitrate Remover by Juwel, encourage bacteria to reduce nitrate from within. Whereas, the chemical versions actually absorb it. Both types are useful for getting a quick biological boost in a new setup.

5. Overstocking and Overfeeding

Our aquarium guide for beginners explains more about feeding fish and stocking the tank. But, it's fair to say that most starters tend to give their pets too much food and they stock the tank with too many fishes.

Put another way:

The aquarium nitrate levels should correlate to the amount of ammonia produced by the fish. Hence, more fish will produce more nitrate.

So, the best way to avoid having chronic nitrate problems in the fish tank is to avoid overstocking it with too many fishes - and not to overfeed them.

Check out our easy fish care guide for more information about why keeping fewer fish results in less ammonia, fish waste, and subsequently a reduction in nitrate levels.

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