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Why are water changes not lowering nitrates in my fish tank?

You find that changing the water in your fish tank could help with this problem. After a few rounds of water changes, you’re still faced with high nitrate levels in your tank – Why is that so?

High nitrate levels are also known as ‘old tank syndrome’ in a fish tank, can be hazardous for your marine life, preventing growth, causing stress to the fish, and potentially killing them. Aquarium hobbyists are left wondering why regularly changing the water isn’t lowering nitrate levels. 

In order to truly lower the nitrate levels in your fish tank, not only should you be regularly changing the water, but you should also be employing a few other simple solutions like using a chemical filter, introducing live plants to your tank, installing a powerhead, using a refugia and utilizing microbes.

Keep reading for our guide on how to use these tips and tricks, quickly lower nitrate levels in your tank – giving your fish a happy, healthier life!

Three Reasons Why Regular Water Changes Did Not Lower My Nitrate Levels

While high nitrate levels within your fish tank can be a little bit scary, there are plenty of things you can do easily to ensure your fish are in a thriving environment. The first thing you’ll want to identify is why you might have high nitrate levels in your fish tank. 

By considering a few of the following points, you’ll be able to pinpoint what might be causing your problem and nail down the best solution for your home aquarium.

Let’s dive in!

You Might Be Overfeeding Your Fish

It doesn’t matter how often you’re cleaning your tank – if the fish are being overfed, it will undoubtedly lead to high levels of nitrate in production. If you think this sounds like you, you aren’t alone. Most aquarium enthusiasts feed way too much.

An excellent way to indicate this is to look for leftover food reaching the bottom of the tank. Slow down and feed smaller amounts over more extended periods.

The more the fish eat, the quicker they’ll produce nitrate – and if changing the water is the only thing you’re doing, it won’t be enough to keep the nitrate levels low.

There Could be a Lack of Plants in Your Aquarium

Live plants are an excellent way to get a handle on the nitrate levels in your tank. Plants use nitrate as a fertilizing agent, locking it in until they die.

Consider adding a Duckweed plant to your tank. Not only does duckweed look beautiful, but it’s also one of the easiest plants to grow in your tank. Duckweed is especially ideal for goldfish tilapia and koi fish, getting most of its nourishment from the air.

Your fish will also enjoy the environment that they get out of plants – they like to hide and play around with plants in a fish tank.

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fish tank with no plants
fish tank with no plants

You’re Using High Nitrate Tap Water

Again, it won’t matter how often you’re changing the water out of your fish tank if you’re not using the correct type of water. Specifically, tap water will commonly contain higher levels of nitrate. Some places in the United States have tap water containing nitrate levels at 40 ppm; you must test the water before introducing it to your tank.

As a general rule of thumb, you want to use water below 25 ppm. This level mimics water closer to what fish experience in nature and will be far more likely to thrive in your tank if these levels are appropriately managed.

Measuring your water is crucial to keeping nitrate levels to a minimum.

Five Steps to Achieving Lower Nitrate Levels

So, the regular water changing isn’t entirely cutting it. Your nitrate levels are up, and you’re starting to panic. Take a deep breath and read about the following simple steps that you can take right now to solve your problem!

Use a Chemical Filter

We’ve already stressed the importance of making sure you’re using the correct water for your fish tank, but let’s discuss a few other things to consider while you’re changing the water.

When changing your water, do so using a chemical filter. These specialized filters trap fish food debris and organic particles – all things known to cause higher nitrate levels in your tank. Along with removing nitrate from your tank, a chemical filter also takes care of the phosphate that might be present in your tank.

It doesn’t matter what kind of aquarium enthusiast you are; chemical filters will work in freshwater and marine aquaria environments. On top of this, these filters are long-lasting and won’t need to be changed very often. 

Using a chemical filter is a simple, low-maintenance step you can take to reduce your nitrate levels.

chemical filter for aquarium
chemical filter for aquarium

Introduce Live Plants into Your Tank

In conjunction with making sure that you’re correctly changing the water in your tank, you’ll also want to monitor the pH levels that your tank is facing. The goal here is to make the pH and nitrate levels close.

The pH levels of your water determine how much waste and decomposing fish food will become ammonium or ammonia. Ideally, you can keep pH levels of 7, balancing out with its nitrate counterpart.

We mentioned this earlier, but it’s a great idea to introduce live plants into your aquarium. Certain aquarium plants are extremely helpful in processing the excess nitrate in your tank and can do so without any additional work from you.

Install a Powerhead

Another way to prepare your tank to support life is to install a powerhead that facilitates water movement. The powerhead works well with your chemical filter, as part of its purpose is to push water towards the filter.

Along with this, a powerhead is an excellent way to create current and aerate the water, helping to keep your tank clean and healthy. A powerhead can also save you from purchasing an air pump or air stone.

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Institute a Refugium

A refugium acts as a reservoir in your fish tank that ultimately collects particles, bits, and bacteria, keeping them out of the recirculation of your tank. Commonly, a refugium will have a large reservoir containing a deep sand or gravel bed. Using a complete spectrum light system, a dense carpet of seaweed will grow over the bottom.

The deep sand beds that come from a refugium ultimately serve to give you more control over the nitrate levels in your fish tank. These robust sand beds host a variety of highly beneficial anaerobic bacteria; this reservoir metabolizes excess nitrate, keeping your tank much cleaner and healthier.

Additionally, the reservoir of a refugium grows highly beneficial macroalgae that work to fight off unwanted microalgae. The good macroalgae will increase large enough to fill the tank, providing shade, which decreases the growth rates of bad microalgae.

A refugium will also make your tank appear a little bit cleaner by concealing sediment pooling that naturally occurs in most fish tanks. When a refugium is planted correctly, it will act as a sediment sink. Slowing down the water flow as it passes through, detritus begins accumulating at the bottom, where it becomes consumed by deposit feeders.


Utilize Microbes

There is such a thing as good bacteria, not the kind that will make you sick, but the kind that will help keep your fish tank healthy and thriving, also known as microbes. Some bacteria are even considered a necessity for a healthy fish tank.

Dissolved organic substances in your fish tank are what eventually lead to higher nitrate levels; adding microbes, or good bacteria, to your aquarium can do so much for the typical aquarium enthusiasts.

To keep good bacteria in your tank, you’ll have to create an ideal living space. The simple use of non-toxic, high-surface-area biomedia will provide a sizeable habitable space and allow for a synergistic relationship between the two different types of microbes.

Using an EcoBio-Block is one of the easiest ways to introduce good bacteria into your tank. An EcoBio-Block is a mineral-rich porous stone containing nutrients and benefits that multiply within the block for years. This water clarifying product is reasonably priced and easy to get your hands on. This method is advantageous if you find yourself without enough time to change the water frequently.

Let’s Wrap This Up

With excess nitrate still present in your tank after regularly switching the water out time and time again, you could be left wondering what you’re doing wrong. While changing the water consistently is essential, there are still other techniques that you should be using to promote the healthiest tank you possibly can.

Remember, the first thing you’ll want to do is come up with a diagnosis as to why you’re facing this problem. Try a few of these methods out once you have a good idea of where the high nitrate levels are coming from! More than likely, you’ll be left with a clean tank and happy fish!