If you’re using an external filter for your aquarium, chances are you’re using either a canister filter or a trickle filter. Other filters are generally internal filters: Even an “external” power filter (a hang-on back filter) is partially submerged in the tank. While external filters have their benefits, they also come with a host of questions — one of which is whether these filters need to be placed below your fish tank for best results.
External canister filters should be placed under the fish tank for best results. However, this is dependent on the height of the filter. On the other hand, trickle filters are placed next to the fish tank, not under it.”
In this article, I’ll explain how canister and trickle filters are placed in your tank. I’ll also explain why canister filters should generally be placed under your tank, so you’ll know what steps to take to get the most out of them.
Where and Why To Place Canister Filters
As mentioned above, external canister filters should ideally be placed under the fish tank.
To understand why they should be placed under your fish tank, you must first understand how canister filters work. These filters essentially draw out dirty water from your tank, run it through the filter, and then return it to the tank through a pump.”
While the canister uses a pump to return the water to the tank, the water is initially drawn into the canister due to gravity. So, if the filter needs to work, it should be placed under the tank, ensuring gravity can do its job effectively.”
That said, there are cases where you can get away with placing the canister next to your fish tank rather than underneath it. This happens when you have a relatively tall tank — tall enough that gravity still transfers water from the tank to the filter.”
However, this method has its risks, and those who try this frequently find the canister doesn’t work as efficiently as it would when placed under the tank.
Your canister filter should come with instructions indicating how far below the tank the filter should be placed. The placement can be anywhere from 8 inches (20.32 cm) to 54 inches (137.16 cm) under the tank, depending on the brand and model of the filter.
The brand-recommended position is where the filter will be most effective, so try to place your filter according to these instructions as much as possible.
Once you’ve chosen where you’ll be placing your canister filter, you should then:
- Prep the filter by installing the different filtration media: mechanical, biological, and finally, chemical.
- Prepare the intake tube, the section that draws out water from your aquarium and into the filter.
- Prepare the output nozzle, the section that will transfer the filtered water from the canister back into the tank.
- Start your filter and confirm that everything is working correctly.
Where and Why To Place Trickle Filters
Aside from the canister filter, the other genuinely external filter variation is the trickle filter.”
These filters are also known as wet or dry filters. Like canister filters, they collect dirty water from your tank, filter it, and return it to the tank. However, while the basic premise is the same, they function relatively differently.”
Unlike canister filters, trickle filters don’t need gravity to draw out the dirty water. Instead, they depend on an overflow — that is, a mechanism that prompts water to flower out of the tank and into the filter once it hits a predetermined level.
Once the water is in the tank, it falls over (or trickles down over) the filtration media. The clean water falls into and is collected in a sump at the bottom of the filtration media. From there, it’s transferred to a pump and then pumped back into the tank.
Because this type of filtration system doesn’t require gravity to transfer water from the tank to the filter, they don’t need to be placed under the fish tank. Instead, they’re installed next to or (ideally) above your tank, depending on their size.”
To get a better idea of how a trickle filter is positioned, take a look at the YouTube video below. It also explains how to set up your trickle filter:
Final Thoughts
The external filter should ideally be placed under the fish tank if it’s a canister filter. However, if your external filter is a trickle filter, placing it under the tank is unnecessary. Canister filters require the action of gravity to work effectively, while trickle filters do not — hence their respective recommended positioning.
