Where Does A Filter Go in A Fish Tank—Can It Be Submerged

Where Does A Filter Go in A Fish Tank—Can It Be Submerged

AquariaWise is a participant in the Amazon Associates program and a few other affiliate programs and may earn from qualifying purchases at no extra cost to you. However, we have vetted every program in this guide and believe they are the best for generating affiliate revenue. You can read our full affiliate disclosure in our privacy notice.

When new to fish keeping, things that seem obvious to others may be quite tricky for you. Plus there is no shame in wanting to get more from your equipment, even when you have a lifetime of fish keeping experience.

Thus, if placing your aquarium filter in a different space in the tank will guarantee better water clarity, that’s a welcome change, yes?

In that light, what is the best place to place your aquarium filter?

Now, there are various types of aquarium filters that you can get, suited for different applications and budgets, and each sits differently in the fish tank.

The simplest and most common of all is the internal filter, which sits in the corner of the aquarium. Most are driven by an air pump that sucks the water past the media.

This filter type is also called a sponge filter or internal air-driven aquarium filter or corner filter.

You may also come across a hang-on filter, which as the name suggest, hang on the back of the tank and pass the water via filter material driven by a cartridge.

Another choice is the undergravel filter, which sucks the water down through the substrate, Bacteria grows on the gravel and breakdown the waster from your fish.

Obviously, this type of filter go at the bottom of the tank under the substrate.

For large aquariums, canister filters are quite popular, and because they are quite big, they sit outside the fish tank with just a hose going to and from the aquarium.

You can easily conceal them in a cupboard.

That said, you may want to make sure your filter sits next to the heater such that the water flow distributes the heat around your tank and keep a constant temperature.

For better insight, please read on.

How High Should Your Filter Be in The Fish Tank?

How you place your fish tank filter will still depend on the type of filter unit you have.

When considering an air-powered-sponge (corner) unit, you just need to ensure it’s well below the water level making sure the bubbles rise sufficiently to draw the water through the filter media.

An undergravel filter is not too much of a challenge to position, because it must go under the gravel whichever way you look at it.

However, please note that it’s only the perforated plate that sits under the gravel, the uplift tubes with the porous diffuser and air pump do not.

The undergravel filter tube rises on one corner of the tank into an air pump outside the aquarium. For best results, place the pump near the top of the fish tank (water level) to keep the water from flowing back into the pump in case of a power failure.

Hang on back filters must be placed higher than the water level because while the design may vary, the principal is the same.

Water is drawn from the aquarium and pumped into a filter box, then flow by gravity through a slip-in cartridge back into the tank.

When its a canister filter you have, the output should sit about 1.5 to 2 inches below the water surface (fully submerged) pointed to the surface for better agitation.

If you place the canister filter above the water level, there will be a lot of splashes, which apart from going everywhere, they make quite the noise.

Should Your Fish Tank Filter Be Fully Submerged?

Depending on the type of unit you have, your aquarium filter can be either be above water or under the water.

Internal filters must be fully submerged to work correctly. They work best near the substrate, though if the air pump is separate, it is usually situated somewhere outside the fish tank.

For this reason, most sponge filters come with suction cups to help hold the unit in the desired corner of your aquarium.

Hang on units, unlike internal filters, should sit above the water level because (as mentioned), the flow back into the aquarium is by gravity, meaning the unit needs to be at a higher position to work correctly.

As for undergravel filters, the perforated mat must be fully submerged and covered with gravel, but the air pump should be somewhere outside the aquarium connected to the mat through a tube.

Lastly, a canister filter cannot be submerged because it sits outside the tank by design.

That said, corner filters and undergravel filters are quite useful when you need more agitation in your aquarium because they are submersible, hence create a current inside the tank, which helps circulate oxygen all around.

Even so, internal filters are only ideal for smaller fish tanks, for large aquariums, you may want to get a canister filter or a hang-on-back unit at the very least.

Add an air pump to aerate larger fish tanks.

How Do You Know If Your Fish Tank Filter is Working?

Once you have positioned your filter the right way, you will surely need to know whether it’s working optimally or not.

The most obvious sign of a functional filter is water movement, so if your equipment is buzzing, but the water remains still, your unit is most likely not working as it should.

Another common sign of a faulty unit is a rattling sound coming from the filter, albeit some internal filters make a rattle just a bit when you turn them on, as the water is introduced.

Usually, the rattling sound is caused by a broken piece of the filter inside the unit. In which case, unplug it and give it a light shake to see if any loose objects are moving inside.

It’s also quite common for old or dirty components to make aquarium filters function slowly and eventually ware them down. So, if you are sure there are no broken parts, try cleaning the filter media and cartridge or change them where need be.

Moroever, look for any cracks on your filter’s facade, they could compromise the function of your unit, especially if the split goes all the way to the inside of the equipment.

Away from that, the other way to tell if you filter is working as it should is to just look for flowing water because with some units such as hang-on-back and power filters, you should be able to see the water coming out.

You can even take the part of your canister filter that goes in the tank to see if the output is getting any flow. Plus, sometimes the unit will cause a visible ripple, meaning when it’s there, your filter is working correctly.

Lastly. please note that just because there is a flow of water from your filter unit, it does not mean it is working optimally.

And as I said, part of the reason this may be so is a dirty filter media, thus make sure you clean yours at least once every week or whenever you suspect your filter is clogged.

Eddie Waithaka

Resident Content Creator and Marketer at AquariaWise who talks about aquariums and fish and aquascapes a lot.

Author image

AquariaWise Newsletter

Get exclusive the tips, that we only share with our subscribers. Enter your email address below.

Your subscription could not be saved. Please try again.
Your subscription has been successful.

This site uses cookies. By continuing to browse the site, you are agreeing to our use of cookies. Okay, thanks