The Aqua One Ocellaris 400 is a compact external canister filter designed for smaller aquariums up to approximately 100 litres.
With a flow rate of 400L/hr and 2.5 litres of filter volume, it gives smaller tanks the advantages of external filtration without taking up valuable space inside the aquarium.
It comes supplied with mechanical and biological filter media, making it a great option for tropical, coldwater and smaller marine aquariums where you want clean presentation and flexible filtration.
Why Choose the Ocellaris 400?
The biggest advantage of the Ocellaris 400 is its compact size.
Instead of having a bulky internal filter sitting inside the aquarium, the canister sits outside the tank while the inlet and outlet remain inside.
This gives you:
More usable space inside the aquarium
A cleaner-looking setup
Mechanical and biological filtration
2.5L of filter volume
Customisable filter media
Quiet and energy-efficient operation
Only 6.7W power consumption
Replacement media and spare parts available
It's an excellent little filter for someone who wants to move beyond basic internal filtration without needing a full-sized canister filter.
Who Is It For?
We recommend the Ocellaris 400 for:
Smaller tropical aquariums
Coldwater aquariums
Planted tanks
Aquariums up to approximately 100L
Customers wanting equipment outside the aquarium
Tanks where internal space is limited
Aquascapes where you want less visible equipment inside the tank
For a heavily stocked aquarium or a tank close to the maximum 100L rating, we'd consider stepping up to the larger Ocellaris 850 rather than choosing filtration purely from the maximum tank-volume figure.
Which Ocellaris Model Should I Buy?
Ocellaris 400 Up to approximately 100L 400L/hr flow Best for smaller aquariums.
Ocellaris 850 Up to approximately 250L 850L/hr flow A substantial step up for medium-sized aquariums.
Ocellaris 1400 Up to approximately 400L 1400L/hr flow Designed for larger aquariums requiring considerably more filtration capacity.
If you've got a normal aquarium comfortably below 100L, the Ocellaris 400 is the compact option.
If you're right around 100L with a heavy fish load, messy fish or plans to upgrade tanks later, we'd lean toward the 850.
Filter Media Included
The Ocellaris comes supplied with:
Filter wool
Mechanical filter sponges
Sintered glass biological filter media
This gives you mechanical and biological filtration straight from the box.
The modular media design also allows you to customise the filter with other media if your aquarium requires something different.
Important First-Setup Tip
Open the filter and check all of the media before you turn it on.
Make sure you remove any plastic wrapping or packaging from the filter media inside the canister before starting the filter.
It sounds obvious, but we see people accidentally leave biological media sealed in the plastic more often than you'd think!
Give the media an appropriate quick rinse, arrange everything correctly inside the canister, then reassemble the filter before starting it.
How Do I Set It Up?
Open the canister and check the supplied filter media.
Remove all plastic packaging from the media.
Rinse the media where appropriate.
Make sure the media and internal components are seated correctly.
Position the canister below the aquarium.
Install the inlet and outlet pipework.
Make sure the hoses aren't kinked.
Fill/prime the filter using the Ocellaris 400 priming system.
Check all fittings and seals.
Switch the filter on and confirm water is flowing correctly.
The Ocellaris 400 uses a priming cap, rather than the manual primer used on some of the larger Ocellaris models.
How Often Should I Clean It?
There isn't one fixed maintenance interval that works for every aquarium.
Clean the filter when you notice:
Reduced water flow
Heavily clogged filter wool
Dirty mechanical sponges
Excessive waste accumulating inside the canister
How quickly this happens depends on fish load, feeding, plant matter and how much waste the aquarium produces.
When servicing the filter:
Clean or replace fine filter wool as required
Rinse reusable mechanical sponges
Inspect the impeller and pipework
Check the O-ring and seals
Avoid unnecessarily replacing all biological media at once
Your biological media contains beneficial bacteria that form an important part of your aquarium's filtration.
Specifications
Model: Aqua One Ocellaris 400 Product Code: 94141 Maximum Aquarium Volume: 100L Flow Rate: 400L/hr Filter Volume: 2.5L Power Consumption: 6.7W Dimensions: 18 × 10 × 22cm high Suitable For: Coldwater, tropical and marine aquariums
Replacement Media & Spare Parts
Replacement parts are available for the Ocellaris 400, including:
Replacement sponge
Replacement filter wool
Impeller
Pumphead O-ring
Pumphead
Inlet set
Outlet set
Being able to replace individual wear parts is one of the reasons we prefer proper aquarium filters over equipment that effectively becomes disposable when one small component fails.
Simply Fish Recommends
We think the Ocellaris 400 makes the most sense when you've got a smaller aquarium but still want the benefits of an external canister filter.
For planted tanks and aquascapes in particular, getting the filtration equipment out of the aquarium gives you a much cleaner look and frees up internal space.
The main thing we'd watch is aquarium size.
Although Aqua One rates it up to 100L, we wouldn't automatically put the smallest possible filter on a heavily stocked 100L aquarium. If you've got lots of fish, species that produce significant waste, or you're likely to move into a bigger tank, we'd step up to the Ocellaris 850.
For a lightly to normally stocked smaller aquarium, though, the Ocellaris 400 is a compact and tidy filtration option.
FAQ
What size aquarium is the Ocellaris 400 suitable for? Aqua One rates it for aquariums up to approximately 100 litres.
What is the flow rate? The manufacturer's specified flow rate is 400L/hr.
Does it include filter media? Yes. It comes supplied with filter wool, mechanical sponges and sintered-glass biological media.
Do I need to remove packaging from the filter media? Yes. Open the canister before setup and remove any plastic wrapping or packaging from the media before operating the filter. This is an easy setup step to miss.
Is it suitable for planted aquariums? Yes. It's particularly appealing for planted tanks because moving the main filter body outside the aquarium reduces visible equipment inside the tank.
Is it suitable for marine aquariums? Yes. Aqua One lists the Ocellaris 400 as suitable for coldwater, tropical and marine aquariums.
Does it have a primer button? The Ocellaris 400 is different from some of the larger Ocellaris models and uses a priming cap rather than the manual primer system.
Should I choose the Ocellaris 400 or 850? For smaller aquariums comfortably below 100L, the 400 is the compact choice. If you're near the 100L limit, heavily stocked or expect to upgrade your tank, we'd seriously consider the 850.
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