8. Review of Aquarium Filters

One Big Scam

Any discussion of ANY filter requires a disclaimer. ALL commercial filters almost without exception tell the owner to replace the filter media (Cartridges, sponge, ceramic rings, carbon, Matrix, etc.) on a regular basis, once a month, once every three month or once every six months. Supposedly this is because the media becomes clogged and dirty. And the media is ridiculously expensive. We must emphasis:

Replacing the Filter Media is a Big SCAM!!! 

Yes, there is absolutely no reason to replace the media on a regular basis other than to make a lot of money for the supplier of the filter.

Crayfish neon red Procambarus clarkii
Crayfish neon red Procambarus clarkii

Review Of Aquarium Filters

Every aquarium needs a filter to do the biofiltration. These filters have many different aspects which need to be considered.

Filter# of 3″ fish crystal clear*Media capacity cubic inchesMedia capacity cubic centimeterCostLooksLeak potential
Cartridge internal04-1065 – 165DecentNone
Cartridge Hang-on-Back05-15100 – 245GreatCommon
Airlift sponge2 – 860-2001.000 – 3.250BadNone
Sponge with pump3 – 1060-2001.000 – 3.250BadNone
Matten corner5 – 8100-1601.650 – 2.600BadNone
Bottom-to-top Hang-on-back filter10 – 20180-2603.000 – 4.250€€GreatCommon
Undergravel with airlift15 – 301000-200016.000 – 32.000GoodNone
Undergravel with pump20 – 401000-200016.000 – 32.000GoodNone
Canister filter25 – 50500-10008.200 – 16.400€€€GreatCommon
Static sump100 – 3002000-600032.000 – 100.000€€€€ **GreatSome
Fluidized sump200 – 6002000-600032.000 – 100.000€€€€ **GreatSome
* Assumes a good filter media (foam, plastic pot scrubbers or K1)
*** A DIY sump can be made quite cheaply

*# of 3″ Fish refers to the number of three inch fish that can be given crystal clear water with this filter. Ammonia oxidation is much easier than crystal clear water so for ammonia oxidation multiply the numbers by ten to twenty. Note this chart is a very very gross approximation. Also this review assumes a typical 29 to 40 gallon tank with correspondingly sized filters. And it assumes that an overflow siphon is not visually objectionable while a dirty sponge sitting in a tank is objectionable.

This is a very simplistic analysis which won’t satisfy the dedicated hobbyist.

To go into filters in a much deeper review go to the following link:

8.1. Review of Types of Filters in Depth

Auloncara koningsi Mbenji
Auloncara koningsi Mbenji

General Comments on Types of Filters

The larger the fish and the more fish the more cubic inches of media are needed. All these filters have their pluses and their minuses. Which one you use is a matter of personal preference and wallet size.

Personally I love under-gravel filters and have always had them on ALL my tanks. I find hang-on-backs to be very poor performers compared to under-gravels and I haven’t owned a hang-on-back in many years. And sponge filters are great for breeding tanks but kind of ugly in decorative tanks. Large tanks (>75 gallons) with lots of fish and/or large fish do best with sumps.

Many hundred million dollars of research in recirculating aquaculture systems (RAS) has clearly established that two or three chamber K1 Fluidized Bed Sumps are two to four times better on a cubic inch per cubic inch basis of filter media than any other filtration system.

Petrotilapia genalutea Luwala
Petrotilapia genalutea Luwala

Hang-on-back filters are sometimes the only option for folks, especially for small tanks. Cartridge hang-on back filters (or cartridge in-tank filters) are very poor for biofiltration. They will oxidize ammonia but they won’t give crystal clear water. They are especially bad if one replaces the cartridges once a month like the directions say (this is simply one big scam to make money!).

For hang-on-back filter optimization Corey’s (Aquarium Co-op) has an excellent video. It’s a great video from a guy who knows his stuff. He recommends replacing the media, cartridges and baskets with foam blocks and adding foam pre-filters to the inlet tube. This will decidedly improve any hang-on-back filter.

Neocaridina davidi Blue Shrimp
Neocaridina davidi Blue Shrimp

Test of Filters

A test of the ammonia oxidizing capability of various filters was tested with the media recommend for use with them, except that any mechanical filtration such as Polyfil or 40 ppi foam was not used. The various filters and their ammonia oxidizing capabilities tracked very closely to their filter media surface area. Cartridge filters and hang-on-back filters did not do well, canisters and under-gravel filters did moderately well, and the sumps did great.

Auloncara stuargranti Galeriya reef
Auloncara stuargranti Galeriya reef

Filter Ammonia Oxidation Test Results

Ammonia was added to aquariums with various filters. The resulting ammonia levels were measured three days later, and the amount of ammonia added adjusted according to the measured ammonia level. These are the results:

Milliliters dilute Ammonia solution oxidized

FilterAverage15 days30 days45 days60 days75 days90 days
1 inch of gravel0,50.250,50.50,2510,5
Cartridge HOB3,8142484
Sponge Filter84481688
Bottem flow HOB184832163216
Static sump8183264128128128
Fluidized bed sump131166412864256256

The “average” number represents the number of three inch fish each filter can give crystal clear water with. The number of three inch fish that can have their ammonia oxidized is about twenty times this number. Ammonia oxidation is much easier to obtain than crystal clear water.

Note that the “One Inch of Gravel” in this test fairly well puts to rest the idea that the substrate in an aquarium acts as an ammonia oxidizer. This idea is a myth, per this test. Note that 0.5 is the ammonia that a few three inch fish would put out, so it is possible to have an aquarium with no filter in it and no ammonia. It’s just that the stocking must be very light. A gravel substrate is a very weak biofilter.

This test can be reviewed at this link:

8.1.1. Filter Test

Aulonocara baenschi benga
Aulonocara baenschi benga

Discussion of Results

This test is easily performed by anyone who wishes to duplicate it. The average numbers would appear to be representative of the number of four-inch fish this filter can give crystal clear water with (after 90 days with no cleaning). To get the number of four-inch fish for which these filters will remove the ammonia one needs to multiply the average number of fish by twenty. Ammonia oxidation is twenty times easier than obtaining crystal clear water.

Myths About Aquarium Filters

There are many myths parroted around social media about filters. These myths include:

  • The brown “gunk” inside the filter bio-media or filter foam is trapped feces and it is beneficial to the aquarium to remove it frequently and thoroughly. This is the single most damaging myth in the Hobby.
  • Hang-on-back filters which use cartridges, such as Marineland Penguintm, Aqueon Quietflowtm, Tetra Whispertm and Fluval Aqua-Cleartm, should have the cartridges replaced every month to three months.
  • Filters should be cleaned at least every month.
  • Filters and sponges must be cleaned in aquarium water and never in chlorinated water.
  • Under-gravel filters don’t work well.
  • Hang-on-back filters are filters which give great biological filtration.
  • Most canister filters filled with the media that comes with them (typically ceramic rings and bio-balls) are great biological filters.
  • As long as the filtration is adequate to oxidize ammonia, more filtration will not help the health of the fish.
  • The larger the filter the less nitrates in an aquarium and the fewer water changes required.
  • There are bad types of filters called “nitrate factories”.
  • Under-gravel filters need lots of maintenance.
  • Only the flow rate in gallons per hour determines filter efficiency, not square feet of bio-media surface.
  • A canister which has an actual flow rate of 600 GPH (gallons per hour) can filter roughly twice the amount of fish that a canister that has an actual flow rate of 300 GPH.
  • “K1” fluidized beds take longer to cycle than standard submerged beds.
  • “K1” fluidized beds are not efficient as submerged static media beds.
  • Trickle filters are very efficient filters.
  • Wet/dry filters are very good efficient filters.
  • There are anaerobic nitrate removing reactor designs commercially available which work well in the aquarium.

All these myths are simply false!

picture of an aquarium fish Labeotropheus fuelleborni Red Top Thumbi West OB
Labeotropheus fuelleborni Red Top Thumbi West OB

The following sections try to explain the different choices one can make in far more depth:

8.1. Review of Types of Filters

8.2. Hang-on-back Filters

8.3. Canister Filters

8.3.1. Canisters in Depth

8.3.2. Do-it-yourself Canisters

8.3.3. FX Series Canister Filters

8.4. Sponge Filter

8.5. Under-gravel Filters

8.6. Sumps

8.6.1. Sumps in Depth

8.6.2. Static Submerged Media Sumps

8.6.3. Trickle Filters

8.6.4. Wet-dry Sumps

8.6.5 Fluidized Bed Sumps

8.6.6. Do-it-yourself Sump

8.6.7. Foam Sump

8.7. Other Types of Filters

8.7.1. Sand Filters

8.7.2. “High Performance” Filters

8.7.3. Hamburg Matten Filters

8.7.4. Diatomaceous Earth Filters

8.7.5. DIY Bottle Filters

8.7.6. Small Filters

8.7.7. Bottom of Tank Matten

8.7.8. Small DIY Filters

8.8. Sizing Filters and Media

8.9. Anaerobic Reactors

Cyphotilapia frontosa Black Widow Line Bred
Cyphotilapia frontosa Black Widow Line Bred

Return to Home Page

Translated in dutch by : John de Lange