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8.3.3. FX Series Canister Filters

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Author : David Bogert

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Time To Read :
9 minutes
Difficulty : Level 7

Excerpt :

The FX Series Canister Filters can be made into excellent aquarium filters.

FX Canister Aquarium Filters

The Fluval FX series of canister filters can either be very poor biological filters or a very good biological filters:

  • If you follow the Fluval directions and clean the foam once a month the FX filters will be very poor biological filters.
  • If you only clean the foam lightly every six months to a year the FX filters will be superb biological filters.

This all has to do with the nature of the “brown gunk” being cleaned out of the FX foam. This brown gunk is very good beneficial bacteria. This brown gunk takes two months or so to become thick enough to be effective. So cleaning it is just about the worst thing one can do to a FX filter.

Cyphotilapia frontosa 6 Stripe Frontosa
Cyphotilapia frontosa 6 Stripe Frontosa

The purpose of the foam is not to filter the water as is often assumed. The foam serves as the habitat for a vast array of microorganisms that include bacteria, archaea, worms, ciliates, flagellates, and many others. These microorganisms live in a community that is based on biofilms. The biofilms are created by bacteria that secret extracellular polymeric substance (EPS), which is often called “slime”. The community forms a bioreactor that processes the waste and turns it into food and energy for its members, and ultimately into organic or inorganic products that are then used by plants, evaporate, or removed by water changes. It takes a considerable amount of time to establish this “filter community”; consequently, it is very important not to disturb it unless absolutely necessary. The brown filter sludge in a filter is for the most part alive and not simply waste. Removing this mud does more harm than good.

Poret Foam Supplier (Swiss Tropicals):

This is probably the most intelligent statement any supplier of aquarium products has ever made.

picture of an aquarium fish Maylandia zebra Makonde
Maylandia zebra Makonde

The problems that come about with cleaning foam filter material frequently are gone over via a test of foam sponge filters:

6.8. Thorough Cleaning Foam

When foam is cleaned it takes one month for the beneficial bacteria colonies to regroup. So cleaning the foam inside a FX filter once a month insures the foam never does it’s job, which is biofiltration, not mechanical filtration.

Flow in the FX Canisters

Aquarium canister filters typically either flow down through a tube and up through the media or down through the media then up through a tube.

The Fluval FX series canister uses a design which takes a while to understand. The flow is down-up-down-up. It is down through a tube, up around the outside of the foam, through the foam and up to the top, then down through the media in the baskets, and finally up through another tube.

Blue Regal Peacock
Blue Regal Peacock

As the water flows up the first time it flows through the foam from the outside of the canister to the inside of the foam ring. This means the maximum surface area of foam being exposed to the flow. This gives great biological filtration. 

This foam comes out to be about 0.2 cubic feet (5.6 liter) of 30 ppi foam in an FX6. This amount of foam will keep roughly one pound (454 gram) of fish healthy and happy. Add to it 0.2 cubic feet (5.6 liter) of good media in the baskets of the FX6 and the figure goes up to close to two pounds (908 gram) of fish. A similar sized canister filled with only ceramic rings and bioballs can give great fish health to on the order of one fourth pound (113 gram) of fish, only 12% of the capacity of the foam.

The FX series canisters are simply a very well thought out design which gives great biofiltration with a whole lot of foam biomedia, IF IT IS RARELY CLEANED.

picture of an aquarium fish Melanochromis joanjohnsonae
Melanochromis joanjohnsonae

Maintenance of the FX series of Canister Filters

Here is the recommended maintenance for an FX6 canister filter:

Recommended FX6 maintenance schedule
Recommended FX6 maintenance schedule

Simply put, this “maintenance schedule” is bull____.  It is designed solely to maximize the profit to Fluval.

Point by Point:

  • Why would one replace the impeller if it isn’t giving one a problem? It only makes money for Fluval.
  • Intake’s are always fine, so why “check and clean”?
  • Ribbed hosing is very difficult if not impossible to “check and clean”. In any case it is recommended to replace the ribbed tubing as it is prone to leaks.
  • “Mechanical foam” is actually the main biological media in the filter. So cleaning it monthly will only give huge problems. And replacing it when it is still perfectly good only makes money for Fluval
  • Bio-foam should only be cleaned when it plugs, as should all foam. And replacing it if it is fine again only makes money for Fluval.
  • The Bio-max ceramic rings are one of the worst biomedias that there is. Throw them out and replace with pot scrubbers or static K1 media. In any case replacing a ceramic media which will last for centuries serves only to make more money for Fluval
  • And the carbon is also useless. Replacing it monthly only makes money for Fluval.

Is there a pattern that can be discerned here? Something along the lines of “makes money for Fluval”. Isn’t the profit motive great?

picture of an aquarium fish Melanochromis auratus female
Melanochromis auratus female

Replacing the FX Foam with Two Layers

There is a YouTube video maker, the “Pondguru” which recommends replacing the foam in the FX series canisters with two layers of foam. This video is pure unadulterated bull****. The Pondguru is espousing the concept of graduated mechanical filtration using foam. The problem with this approach is that 20 and 30 ppi foam is NOT a mechanical filter. It is ONLY a biological filter. It houses the beneficial bacteria in a biofloc.

If the filter media is something like 40 ppi foam the large particles in the aquarium (like feces) water stop at the surface of the foam. This is a mechanical filter. This brown scum film will spread out and become a biofloc on the surface of the 40 ppi foam quite rapidly and trap the smaller particles. This brown film is quite familiar to anyone who has used a polyester floss cartridge. But none of the foam in my FX6’s is 40 ppi foam. It is all  roughly 20 to 30 ppi foam. So replacing it only makes money for the Pond Guru.

Copadichromis mdoka
Copadichromis mdoka

I’ve had many FX filters and I’ve NEVER found a biofloc film buildup on the foam outer surface (i.e. “mechanical filtration”). What I have found in a beneficial biofloc buildup inside the foam.

I gave the Pondguru the lowest rating of ANY YouTube aquarium video maker. Everything he says is solely designed to make money for the Pondguru. EVERYTHING! Do not believe anything he says. The Pondguru sells very high priced foam! Replacing the Fluval foam with another foam thus serves no purpose (other than to make money for the folks selling the foam, like the Pondguru). Do NOT replace the foam in an FX canister until it begins to compress and deteriorate.

The ability of foam to function as a great biomedia is gone into in some depth in the following article:

7.7.2. Foam Media

picture of an aquarium fish Melanochromis chipokae male
Melanochromis chipokae male

FX Impeller

If you compare an FX impeller with a SunSun impeller you will note one very important difference. The blades on the FX impeller are curved. The blades on the SunSun are straight. This reflects the nature of the motor driving the pumps. The FX motor is one directional. It only operates in one direction with what is called a “starter” (there are several versions of this feature). The cheaper SunSun will operate regardless of the direction of the motor.

The more expensive FX motor is thus much more efficient and gives much better flow than the SunSun. BUT the starter is somewhat prone to failure. So one frequently hears “My FX has stopped turning and just hums’. What happened?“. So this is a somewhat mixed bag.

OB Peacock
OB Peacock

FX Tubing

But note that the FX series has one very big problem. The Fluval FX series have ribbed tubing on them. This tubing will spring leaks. Several Facebook folks have had the tubing get pinhole leaks (even in straight sections) or just plain rip apart in service. This is a typical comment:

I love my Fluval FX6 for the job it does, but EVERY TIME we do maintenance on it (like changing the media), the tubes get hairline fractures and start sucking air, or leaking, or both! I am about to replace those crappy hoses for the FIFTH time since last August. At $20 a pop (if I can find it that cheap and no shipping), it’s not worth it.

This ribbed tubing should always be replaced with better flexible schedule 40 tubing available at industrial supply houses or some big box hardware stores. DO NOT replace the ribbed tubing with ribbed tubing for outdoor ponds. That ribbed tubing is almost as bad as the Fluval ribbed tubing. The popular YouTube video maker Joey had some two thousand gallons (7500 liter) of water go onto his floor when some ribbed pond tubing failed.

FX6 aquarium filter hose upgrade
FX6 aquarium filter hose upgrade

The problem with this is that the plumbing at the ends of the tubes can get pretty difficult because the sizing is odd at 7/8ths inch. You may end up with several hose clamps and a lot of tape and silicone adhesive/sealant use. This process, involving the Fluval AquaStop valves and some 7/8ths tubing, is outlined in a YouTube video “Aquarium Plumbing Failure – Post-Mortem and IMPROVEMENT!” by David Hughey. This problem is serious enough that if one does not have some decent plumbing skills, I recommend one does NOT get a FX filter. The leaks are a very real problem.

Note that the clear tubing in the photo above is for illustration purposes only. This type of tubing kinks easily. I use only heavy duty one inch HydroMaxx Schedule 40 White Flexible PVC Pipe with PVC tape and silicone to bring the Fluval male threads to one inch diameter. It is stiffer that the Fluval tubing but it is approved for use in inside home plumbing and will never spring a leak. I had one very … well… pissed off wife when one of my FX filters sprung a leak and ruined a big section of hardwood floors. It cost me a mint to repair it.

Bichir endlicheri
Bichir endlicheri