• 5-stage filtration — two mechanical stages, one chemical stage (activated carbon) and two biological stages (BIOMAX ceramic rings plus a Bio-Screen pad) run water through a genuine multi-stage path rather than a single sponge.
• Clogging indicator — a visible flag on the housing shows when media needs cleaning, before flow drops enough to matter to your fish.
• Wet/dry trickle chamber — water trickles over the biological media rather than being fully submerged, increasing oxygen exchange and supporting the bacteria colony.
• Adjustable flow control — output can be throttled down for slow-flow species such as bettas and fry-rearing tanks, without needing a separate valve.
• 5 W running cost — at 24-hour operation this filter costs roughly $13 a year to run at a 30c/kWh tariff (see Running costs below).
• Rim-mount, no plumbing — hangs on the aquarium rim with no drilling, siphon-priming or external hosing.

Fluval publishes one flow figure for the C4: 900 L/h, measured against clean, unloaded media. Every hang-on filter loses flow as its mechanical pads collect debris and the chemical and biological media compact — Fluval does not publish a separate loaded-media figure for this model, so we're not putting one in front of you. What we can give you is what that headline number actually means once it's mounted on a tank, using simple turnover maths against the rated flow.

As a rule of thumb for hang-on filters, actual delivered flow with media in place and partially loaded typically runs noticeably below the clean-media rating — expect real-world turnover to sit below the figures above, particularly as the clogging indicator approaches trigger point. If your stocking is at the heavy end for a 265 L tank, size up to a Fluval C4 pair or a canister filter rather than relying on the maximum rated volume as a comfortable working figure.

Two numbers matter before you buy: your tank's volume and your glass or rim thickness. The C4 is rated to 265 L and clips to a rim or glass edge up to 3.0 cm thick. Thicker rimless glass, or a tank with an unusually deep top brace, may not seat the clip securely — check your glass thickness against the 3.0 cm limit before ordering.

The unit ships with its full 5-stage media set already fitted: a poly/foam pad, an activated carbon cartridge, BIOMAX ceramic rings and a Bio-Screen pad. No separate media purchase is needed to run it out of the box.

• Suitable for freshwater and marine (fish-only) aquariums up to 265 L, community and lightly-to-moderately stocked setups, and tanks needing a low-flow option for bettas or fry via the adjustable outlet.
• Not suitable for heavily stocked or high-bioload tanks at the top of the 265 L rating, reef tanks needing protein skimming, or aquariums with rim or glass thickness over 3.0 cm.

At 5 W and continuous 24-hour operation, the C4 uses approximately 43.8 kWh a year — around $13.14 a year at a 30c/kWh tariff. Fluval markets the unit as quiet-running but does not publish a decibel rating, so we're flagging that rather than putting a number on it.

Rinse the poly/foam pad in tank water (not tap water) whenever the clogging indicator flags, to avoid killing off the biological colony living on it. Replace the carbon cartridge roughly every 2-4 weeks if you're running it for water polishing, and rinse — rather than replace — the BIOMAX rings and Bio-Screen pad at routine water changes, since these two carry most of your biological filtration.

Sold with Fluval's manufacturer warranty, which applies in addition to your rights under Australian Consumer Law. Standard parcel freight applies; no special handling is required for this item.

Does the Fluval C4 come with media, or do I need to buy it separately?

It ships with all five media stages already installed — a poly/foam pad, activated carbon, BIOMAX rings and a Bio-Screen pad — so it's ready to run on arrival.

Can I slow the flow down for a betta tank?

Yes. The C4 has an adjustable flow control on the outlet, which lets you throttle output for low-flow species without adding a separate valve.

What glass thickness does the C4 clip fit?

Up to 3.0 cm (1 1/8 in). Measure your rim or glass edge before ordering if you're on a rimless or unusually thick-glass tank.

How do I know when to clean the filter?

The housing has a built-in clogging indicator that flags visually once flow starts dropping, rather than leaving you to guess from water clarity alone.

Is 900 L/h enough for a 265 L tank?

It's the maximum rated volume, giving roughly 3.4x turnover per hour at clean-media flow — adequate for light-to-moderate stocking, but consider a second filter or a canister if you're stocking heavily at that tank size.