Aquarium Filters – How They Work and the Benefits and Negatives of Each Type


There are several different kinds of aquarium filters, each with advantages and disadvantages. Most work best when used in combination to compliment each other, this redundancy is also important for peace of mind in case one filter fails, another will keep your aquarium filtering. I give my opinion too with each of these types of filters, based on 28 + years maintaining a Large Aquarium maintenance company in Los Angeles, California. I used many different types and brands of filters during this time, and continue to try new ones out.


An old standby that is good for biological filtration (the conversion of fish waste from ammonia and nitrites to less harmful nitrates), but is poor for mechanical filtration (the removal of debris- organic and inorganic). Although I have use many over the years with good results, I do not generally recommend them anymore. Most also do not perform chemical filtration although some have small carbon cartridges that go on the exhaust of the lift tube (Lee’s makes such a UGF). They are also not real good for planted aquariums; the roots have a hard time thriving with the filter plants just below the gravel (although you add potted aquarium plants to aquariums with UGFs). UGF are also poor at denitrification, as they do not allow for the fine sand and anaerobic bacteria needed for Nitrate removal.

If used, I recommend a HOB (power filter) as a compliment, they have better mechanical and chemical filtration, but tend to be lacking in biological filtration (some are better than others for this).


Another more popular filter now, these filters are good for mechanical and chemical filtration, and sometimes biological filtration. This does vary widely with the model though. The Aqua Clear is better than most for biological filtration, but it’s design tend to lead to flow-by, resulting in poor mechanical filtration (they also have poor impellers, and in my experience, have a higher than normal break down record). The Penguin has good mechanical filtration (little flow-by), but are not as good for bio filtration, EVEN with the Bio-Wheel! I have run many Penguins since they came out, but their bio-wheels tend to stop easily, and I have run ammonia and nitrite tests with heavily loaded aquariums and observed little difference with or without (I added a seeded Sponge filter to these same tanks and observed an immediate improvement in these levels).
Whisper and ReSun use cartridges that are best rinsed in used aquarium water, or else should have a small sponge placed in them to preserve bio colonies, otherwise these would be my HOB of choice.

HOB filters are good compliments to sponge filters or under gravel filters.


Probably one of the most under rated filters available. These filters are excellent biological filters and reasonable mechanical filters. They are simple and inexpensive. The type of sponge material makes a large difference in the filters bio capacity. Reticulated filter foam is the preferred sponge material. One of the sponge filters benefits is their ease in cleaning, which in turn lowers the amount of organic material being broken down in the nitrogen cycle. It takes only minute to clean a sponge filter by rinsing it used aquarium water, while it may take half an hour to clean a canister filter.

Internal filters and HOB small aquariums are good compliments to sponge filters. Canister filters are good compliments to sponge filters in large aquariums.
I have a lot more information about sponge filters in my article: “Sponge Filters”


Not as common a filter but a much less alternative to expensive and bulky canister filters. Internal filters are basically a power head with a filter of varying capacity attached. They are useful for improved water circulation, generally are good mechanical and biological filters (although generally they do not have a large capacity). They are a great secondary or even third filter in large aquariums, and a good secondary are even primary filter in small aquariums (under 60 gallons).
Internal filters are a good compliment to almost any filter (especially fluidized).
I prefer the Via Aqua internal filters for the flow rates, internal sponges and durability.


Popular filters for larger aquariums in particular, Canister filters are known for their large capacity, which sometimes can be their problem. Many aquarists will not clean canister filters often enough as they are “still running well”, but in reality are have a large build up of organic sludge turning them into ‘nitrate factories”. I do recommend them if they are serviced regularly, as their ability to hold large amounts of different filter media and their excellent mechanical filtration set canister filters above most other filters. For the money I prefer the Via Aqua or Jebo (the Jebo is the same basic filter), the Eheim is excellent but way over priced for the slightly better quality. The Magnum has unique convertible features (the ability to switch between standard canister filtration and micron), but their capacity is poor compared to the rest. Although popular, I am less than impressed with the Fluval. They have weak motors, poorly designed impellers, and have a larger flow-by than most others. I have had dozens of Fluvals on my maintenance route over the years, and their longevity is less than most others.

Canister filters are good compliments to internal and sponge filters.


Popular with marine aquariums in particular, these filters are great biological filters, but poor mechanical filters. They also can become “nitrate factories” like canister filters if not maintained properly.

They are two basic types; the under tank wet/dry which uses a siphon to take aquarium water out to the “sump” where the bio balls are other biological media are, and uses a pump or powerhead to return the water. With this type of wet/dry you want to make sure that you do not over fill the aquarium past where the sump will over flow with the pump off in case of a power or pump failure. This type also usually has a pre filter box to add mechanical filtration to the wet/dry. You can run a variety of bio media in this type of wet/dry. Bio balls and ceramic bio media are popular; live rock, plant refuguiums, sponge filters attached to the pump intake, or all of the above are also popular.

The other type is the built into the back wet/dry. These wet/drys are usually much more reasonably priced (along with the aquarium they are attached to). They usually do not have the versatility or capacity as the under tank wet/drys do though.
Internal filters are usually good compliments to wet/dry filters.


These filters are primarily biological filters only. They work well attached to an internal or canister filer (I prefer an internal). Fluidized bed filters use fine sand kept suspended in a water flow for aerobic biological filtration. The plus is they are basically self cleaning as the sand is constantly rubbing against other grains keeping down the organic buildup. The negative is do not supply a lot of oxygen for the aerobic bacteria. I have set up fluidized filters in marine aquariums in place of wet/drys with excellent results (I set up a whole marine aquarium store department this way). But I strongly recommend other filters (especially internal) to make up for the weakness of fluidized filters. If properly installed, their strengths will shine (they are not the nitrate factories that wet/drys are).


These filters are primarily biological filters. Their advantage is they work both aerobically and anaerobically (removing nitrates). They are not good as the only filter and do not replace mechanical or even germicidal filtration (in marine). They do make an excellent alternative to sometimes difficult to use protein skimmers.


Germicidal filtration is the use of UVC radiation or ozone to kill disease pathogens and improve the Redox Potential in aquariums. I believe they are essential to a healthy marine fish aquarium. But are equally important to expensive and sometimes delicate freshwater fish such as Discus. Many articles I have read state that a UV is not that beneficial to an established aquarium as a healthy aquarium depends on beneficial bacteria typically growing on media in your filter which neutralize ammonia. Unfortunately the problem with this statement is beneficial bacteria belongs in the filter, not in the open water. Also this is great for advanced aquarists who are not adding fish and have a healthy Redox Potential, but not in the real world of average and above average aquarists that I have dealt with in the 100s of aquariums I have serviced.
I have a very in depth article about “Why you should use a UV Sterilizer and how it works” . I strongly recommend reading this article.


Protein skimmers remove nitrogenous wastes (protein based organic waste) via foam refraction. The protein skimmer collects this waste in a cup, where it is then emptied. There are pump driven and air driven models. Protein skimmers generally only work in marine aquariums where they are very popular in reef aquaria, as they are needed to keep nitrates below .20 ppm for the delicate marine invertebrates. The advantages are that they remove nitrogenous waste before they can go thru the nitrogen cycle and become nitrates. The disadvantages are they are messy, take frequent adjustments (at least on many commercial models), and in my experience, over rated. I have kept many reef aquariums successfully with and without protein skimmers (I believe lighting such as metal halide is more important to a successful reef aquarium than a protein skimmer).
The key to keeping low nitrates without a protein skimmer is;

*Proper feeding of foods with highly digestible proteins so as to lower the nitrogenous waste produced.

*Good anaerobic filtration via live rock, live sand, or mud filtration.

*Plant refugiums and or good plant and green algae growth in the aquarium.

*Proper and frequent cleaning procedures. Using a gravel vacuum (or better, the Aquarium Cleaning Machine , which with recirculation of water thru a micron cartridge after the initial water change, insures better waste removal with less water changed.) to remove waste before it can go thru the nitrogen cycle, but not digging so deep so as to disturb anaerobic filtration in the sand (I prefer a layer of fine sand under #3 gravel to achieve this).

By Carl Strohmeyer

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