Why Does My Betta Fish Stay by the Filter? 7 Likely Causes

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Betta fish always require an aquarium filter to remain happy and healthy. But why is your betta spending all of its time hanging out by the filter?

It could be for several reasons, and many of them are related to the principle that betta fish need a filter flow that is not too weak, nor too strong.

But there are other reasons, too. Some of them may surprise you!

Lack of Oxygen

One of the biggest reasons that your betta fish might be hanging out by the filter output is because the tank has become low in oxygen.

This is because the faster flow of water coming out of the filter contains more oxygen than the more stagnant parts of the tank.

Although betta fish have the rare and remarkable ability to breathe oxygen from the water’s surface, they prefer to absorb the majority of their oxygen from the water through their gills. This means that they still require a healthy dissolved oxygen level in the water just like other fish do.

To increase their oxygen supply, keep the tank clean with regular filter changes and tank vacuuming and make weekly or bi-weekly water changes. Also, consider adding an airstone or filter accessory such as a spray bar to increase gas exchange in the aquarium.

Poor Water Quality

As well as low oxygen, a betta fish may hang out by the filter’s outlet to enjoy the slightly cleaner water that’s available there. If the aquarium has become very dirty, the water can become full of toxic waste products such as ammonia and nitrites.

As water is ejected from the filter, it comes out slightly cleaner than the surrounding water and this may be enough to attract a betta that is sick of the bad water quality in the rest of the tank.

Once again, it’s important to keep on top of tank hygiene. Uneaten food is one of the worst culprits for poor water quality.

As well as regular tank maintenance, avoiding overfeeding is one of the most important principles to improve aquarium water conditions and ensure plenty of oxygen.

Enjoying the Filter Flow

Now, it’s important to know that betta fish don’t enjoy strong water currents. With their long fins, betta fish can struggle to swim against a fast flow rate and can even become very stressed and sick in tanks with a strong current.

A weak current, however, may be positively enjoyed by your betta fish. Betta fish with shorter fins, like Plakat bettas and females, are stronger swimmers than males with long fins and may especially enjoy swimming against a current. Think of it a bit like a treadmill – the fish can exert energy and get some exercise while staying in the same spot!

Some types of filters have an adjustable flow, allowing you to change the strength of the current. With this feature, you can dial the filter’s output to just the right strength so that they’ll enjoy swimming against it rather than getting overwhelmed by it.

Escaping the Filter Flow

If your betta fish is hiding behind the filter output instead of in front of it, it might be trying to escape from a filter current that’s too strong for it.

As I just mentioned, betta fish hate strong currents and can even suffer from acute stress and serious health problems if subjected to a strong filter flow rate for extended periods.

If the corner of the tank just behind the filter outlet is the stillest place in the aquarium, a betta may well go there to seek refuge from a current that’s too strong.

If you suspect your betta is avoiding a strong flow rate, you need to reduce your filter’s flow to save your betta unnecessary distress as soon as possible.

If you’re using an internal power filter, a canister filter, or a hang-on-back filter (HOB), you can reduce the filter’s flow by using a filter baffle, a spray bar, or a lily pipe. For tanks of 10 gallons and smaller, I’d recommend using a simple sponge filter.

Check out our guide to the very best betta filters here.

Hiding from Aggressive Fish

why does my betta fish stay by the filter

As well as the above reasons, your betta fish might simply be using your filter as a cover to hide behind.

While bettas can be very aggressive fish, they’re also fairly delicate creatures. Their long fins make them quite vulnerable to attack from other fish who may nip at their fins or compete with them for territory.

If your betta is feeling intimidated by its tank mates, it may seek out places to hide in the aquarium. If there aren’t many other hiding places in the tank, it may take cover behind the filter.

There are two solutions to this issue. Firstly, remove any fish that are nipping at your betta’s fins or otherwise intimidating him.

Secondly, if your betta tank lacks hiding spots, be sure to provide plenty of alternative hiding places in the tank, such as rocks, driftwood, and especially live plants for your betta to hide behind.

Whether your betta is sharing a tank with other fish or not, he will greatly benefit from plenty of hiding places in his tank!

Aquarium Lights or Sunlight Too Strong

In the wild, betta fish often inhabit places with overhanging vegetation and subdued lighting. If your aquarium has particularly high-intensity lights, your betta might be hiding behind the filter to seek shade from the overhead light.

The same can be said for direct sunlight entering the aquarium, which should always be avoided in betta tanks.

Avoid choosing bright lights for betta tanks, and always place your aquarium out of direct sunlight to keep your betta fish happy.

If you don’t wish to change your lighting setup, another solution is to create shadows by adding plenty of live plants and especially floating plants to create a dappled lighting effect underneath.

Feeding Instincts

Our last reason that your betta fish might be spending time near the filter’s output is a natural feeding instinct.

In its natural habitat in Southeast Asia, betta fish sometimes live in the shallow pools of small forest streams. In such a setting, the incoming current to the pool is the most likely place where fresh food will arrive.

This means that your betta may be using its natural hunting instinct in an attempt to seize prey such as aquatic insects and worms that it anticipates getting from the incoming water flow.

You can satisfy your betta’s carnivorous feeding habits by offering him regular helpings of live and frozen foods. Healthy meaty treats such as bloodworms, tubifex worms, daphnia, brine shrimp, mosquito larvae, and mysis shrimp can make a world of difference to your betta’s health, appearance, and general well-being!

Betta by Filter FAQs

How Can I Reduce the Current of My Aquarium Filter?

As mentioned above, some power filters come with a dial that allows you to adjust the flow of your filter’s output.

If there is no built-in control on your filter, you can redirect and disperse your filter’s output by using a filter baffle, a spray bar, or a lily pipe.

You can also reduce the intake current of your filter by adding an extra pre-filter sponge to your filter.

Can a Betta Fish Get Sucked into the Tank’s Filter Intake?

Unfortunately live betta fish can occasionally get sucked into an aquarium’s filter intake. If the filter flow is too strong, it can overwhelm your fish and suck it into the intake, pinning it against the filter entrance.

Bettas with long fins are especially prone to being sucked in by filters because they have weaker swimming ability. As always, choose a filter that either has a gentle flow or one that allows you to adjust the strength of the flow.

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