Fluval C4 Power Filter Review: Is This The Best HOB Filter?

Estimated read time 6 min read

Fluval is one of the most well-known and well-respected brands in aquarium filters, and the Fluval C4 Power Filter is their top-of-the-line hang-on-back (HOB) filter.

Although similar in many respects to their AquaClear line of filters, the C-Series filters offer some upgraded features and better ease-of-use.

With five stages of filtration and a modular media compartment design, the C4 keeps water clear and makes cleaning and switching out media a breeze.

If you’re looking for the best HOB filter look no further than the Fluval C4 and check out the full review below.


Quick Overview Fluval C4 Power Filter

Fluval C4 Power Filter

Get The Fluval C4 Power Filter

The Best Features Of The Fluval C4

  • 5-stage filtration system that does an amazing job keeping your water clean and clear.
  • Its a HOB filter that works much like a Canister Filter.
  • Great media capacity & easy to custom fit custom media due to the large and easy-to-access compartments.
  • The modular compartments make dismantling this filter for scrubbing and changing out media incredibly simple.

What You Need To Know About The Fluval C4

The Fluval C4 Power Filter is a hang-on-back filter that works much like a canister filter.

It has a modular media compartment design that allows you to switch out or clean only one part of it at a time, and it can hold much more media than other HOB filters on the market. The modular design also makes it simple to custom-fit your own media.

The C4 features a 5-stage filtration system (two mechanical, one chemical, and two biological) that does a great job at sifting out particles and filtering out impurities.

Coupled with the high flow rate, this filter is capable of producing amazingly clear water that will keep your fish happy and healthy.

This filter also features precise flow rate control with its patented Refiltration system, which allows you to adjust the flow rate without affecting the filter’s efficiency.

If you decrease the flow, up to 50% of the water in the filter is cycled back through the system, further filtering it and enhancing water clarity.

What Are The Capacities Of The Fluval C-Series Power Filters

The Fluval C4 Power Filter is the largest filter in Fluval’s C-series line of filters that also includes the;

This video goes over all the features and benefits of Fluval C-Series power filter, the world’s only 5-stage HOB filters.

From Fluval Aquatics


  • Excellent water flow to ensure you get the best filtration possible.
  • Modular media compartments make cleaning and switching out media a piece of cake.
  • Five-stage filtration does a great job at scrubbing the water clean.
  • The included bio-media is very easy to clean.
  • Easy to custom fit custom media due to the large and easy-to-access compartments.


  • Dual-sided foam pad needs replacing every few months, but this is mainly because it does such a great job at trapping particles.
  • Spout that trickles water over the the bio-media can be prone to clogging.
  • There are lots of crags and crevices around the impeller that make cleaning it a little tough.

Hands On Fluval C4 HOB Filter

The C4 was clearly designed with quality and efficiency in mind.

There is very little dead space inside the filter, so water has to pass through the filtration media. Everything fits together snugly and the plastic components are high-quality and seem durable.

The star of the show is the five-stage filtration system that Fluval included, which passes your tank water through a cycle of mechanical, chemical and biological filtration:

Stages 1 & 2: Mechanical filtration via a double-sided poly/foam pad. The porous foam side traps larger particles, while the dense poly foam side filters fine debris.

Stage 3: Chemical filtration with activated charcoal removes odors, impurities, and discolorations.

If you prefer not to use activated charcoal in your system, the media basket is big enough for you to substitute another foam pad or other media of your choice.

Stage 4: Biological filtration via a bio-screen at the top of the trickle chamber. This filters out any debris before the water drips into the biological chamber, and ensures that the water flow is evenly spaced.

Stage 5: Biological filtration with C-nodes. The unique “star shape” and porous surface of the C-nodes provide an optimal environment for friendly bacteria to live, and enhances ammonia and nitrate removal.

But how does Fluval’s five-stage filtration actually work?

Amazingly well. This filter keeps tank water crystal-clear, and the high flow rate ensures that all your water is cycled through multiple times per hour.

There is also a built-in cleaning regulator that alerts you when your filter pads become clogged and it’s time for a cleaning.

Speaking of cleaning, the modular compartments make dismantling this filter for scrubbing and changing out media incredibly simple, though there are some nooks and crannies around the impeller that need extra attention.

Here are a few maintenance tips for Fluval C series filter.

From Fluval Aquatics

Buy The Fluval C4 Power Filter

Fluval once again hit a home run with this power filter.

The Fluval C4 combines the greater media capacity and higher flow rate of a canister filter with the lower price and easier cleaning of a HOB aquarium filter to give you the best of both worlds. The five-stage filtration works well, and the filter is both easy to use and easy to clean.

The C-series is a step up from the excellent AquaClear line of filters by Hagen, which Fluval also owns.

While both are great filters, if you have a couple of extra dollars to spend, the C4 is a better choice than the AquaClear for most people.

If you’re in the market for a filter for your 40-70 gallon tank, the Fluval C4 Power Filter should be at the top of your list.

Fluval C4 Power Filter

Get The Fluval C4 Power Filter

Further Reading: If you’re looking for more great filters consider checking out our review on the New Fluval 07 Series Canister Filter which is a seventh-generation product with more than forty years of history and noted as the best selling canister filter of all time.

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