How Deep Should The Filter Be In A Fish Tank?

If you’re using an internal, air powered, or under-gravel filter, then you want it to be at least completely submerged, with all of the filter being visibly positioned entirely under the surface of the water and none of it above the water line.

Will Cloudy Water From Sand Hurt Fi...
Will Cloudy Water From Sand Hurt Fish?

The depth it is positioned at doesn’t really matter, so long as it is totally underwater. Other than that, you can put it wherever you want – in a corner, tucked away and hidden by appropriate tank foliage, is probably the best place.

This is why the majority of internal fish tank filters come with suction cups or hooks to be securely positioned inside without causing harm to the creatures in your tank. DO NOT USE A GLUE OR OTHER ADHESIVE TO HANG THE FILTER!

So long as you can see bubbles clearly rising, and water being efficiently and effectively drawn through the filter, then it’s working correctly. Of course, an under-gravel filter, as the name suggests, is placed beneath tank gravel.

Canister or HOB (hang on back) filters, those that are positioned outside of the tank, are not designed to be submerged. They must always stay outside of the tank, ensuring that the outlet is positioned at least two inches above the water line.

Even if you think it would look better with them inside the tank, it’s not worth the risk. Not only could it impede the function of your filter, but it could also cause harm to your poor fish and their plant friends, too!

How Deep Should The Filter Be In A Fish Tank

How Deep Should My Aquarium Filter Intake Be?

Toward the tank’s bottom! Most fish owners would advise that when you’re using a canister filter for your tank, the intake tube needs to be at least two inches from the bottom. This means water can be sucked up efficiently and quickly cleaned out.

Not only that, but it also prevents any debris from the bottom of the tank, like pebbles or plants, from being sucked into the tube when the filter is in action. Unless you want a blocked tube, keep it a little bit raised above potential obstructions.

You can position it higher up if you like, but the lower it is, the less likely you’ll be able to see the intake screen – an important part of the intake tube that stops your precious fish and other creatures from being taken into the filter accidentally!

Of course, that doesn’t matter to everybody, but some people who keep aquariums like to preserve the most natural aesthetic possible, so anything like visible filters and pipes must be hidden or disguised to avoid ruining the illusion.

There isn’t a strict guideline for depth, so it might take a little bit of trial and error with repositioning in order for you to find the spot that works best for your specific filter system, tubing and tank. As long as it’s clean and the fish are happy – no problem!

Does A Canister Filter Have To Be Below The Tank?

Yes, unless you don’t want it to be installed correctly and filter the way it’s supposed to! A canister filter must always be placed directly below the aquarium, because they require the force of gravity in order to properly function.

Depending on how tall your tank is, you might be able to position the canister beside the aquarium, rather than underneath it, but you’ll find that this significantly weakens the filter’s ability to siphon water, rendering it pretty much useless for the intended function.

It doesn’t necessarily need to be an eyesore, however. You can hide it in a cupboard underneath the tank, provided all of the tubing and the power cord is able to come through the back of the unit somehow and then fed into the water. 

Don’t try and experiment with its positioning either. Standing upright vertically is the best way to ensure the filter functions as it is supposed to, and that your fish will have the nicest environment possible.

Although you can technically lay a canister filter onto its side and it will still function, this will cause the internal filtration system to be less successful, and could cause random contaminants to stay in your water as they sink to the “bottom” of the canister, which is actually its side.

Plus, the components inside the filter will have to work harder in order to function properly, which means they will wear out and break down faster, which means you’ll probably need to buy yourself a new filtration system way sooner than planned.

Given that they can be pretty expensive purchases, you want yours to last as long as possible. Therefore, you should always use it as the manufacturer recommends, and never stray from their instructions unless you want to void any warranty!

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