If you are looking to upgrade your current filter or start up a new aquarium you may be wondering what kind of filtration will work best for your set-up. What follows is some information on selecting the correct method of filtration for your tank. We will explain what your options are, why you would pick a certain filter over another, and why certain filtration may or may not be the best fit your aquarium. We will keep it fairly basic, so of course please feel free to contact one of us if you would like to get into greater detail about anything you read. There is a lot of conflicting information out there and filtration can be confusing but it doesn’t have to be. We aim to simplify this for you. There are other types of filters than the ones presented here, but these are by far the most common methods.
Canister Filters -
This method of filtration is usually the preferred method of any die-hard fish or plant keeper. They are especially popular with people who keep planted tanks on a serious level and by those who keep monster fish species as they are a filter that is able to process much higher levels of waste than any other type of filter. What sets them apart from other filters is the capacity for filtration media that they are able to hold and more importantly the surface area for biological media. This can sometimes amount to 10-20 times what even the biggest power filters can hold. They are the number one choice for the planted tank as the filtered water coming from the filter, into your tank, enters the water column under the surface of the water, keeping Co2 from escaping. Canister filters are also a popular choice because you can hide them from view in your aquarium cabinet or off to the side below the tank. You can customize the intake and output stems to gain an advantage in flow rates in case you are keeping a species that prefers less turbulent water flow. There are output stems that will increase your flow rates too for very large or long tanks where the stock output stem proves insufficient. Canister filters also allow you to utilize “in-line” features such as UV sterilizers and in-line heaters. Another major advantage of a canister filter is low to no bypass. Bypass is water that is able to escape the filter without passing through the filtration media. This occurrence is common in power filters as they usually employ a mechanical pad of some sort that gets clogged over time. Once the pad is clogged even somewhat, the water just goes around the pad and is not filtered. In a canister filter, all the water is forced through the media at all times keeping bypass to a bare minimal.
Advantages - There is a canister filter for every size tank you can think of. They are versatile and customizable, able to handle the heaviest of fish loads, and perfect for the planted aquarium. The ability to add in-line UV sterilization and in-line heaters should not be overlooked. They are easy to clean, inexpensive to upkeep and do the best job at keeping your aquarium in top shape.
Drawbacks - There are hardly any drawbacks to be found if used properly. As with any filter, buying one that is much too large for the the tank you are putting it on is not only a waste, but will surely have too much flow for the fish and/or draw the fish into the intake strainer. Cheap knockoff models are everywhere on the internet. Usually ones that feature built-in UV sterilizers should be avoided as most (there are always exceptions) push water through the sterilizer too fast to be effective at which point the UV sterilizer becomes a gimmick that those looking for a deal will fall for. A canister filter is something that a good local fish store should walk you through when you buy one and help you select the model that is right for your specific tank.
Who should use them? Anyone who places filtration as a top priority in their fishes lives.
Power filters - These are sometimes referred to as ‘hang-on-the-back’ filters. They are now the industry standard and have become the most popular way to filter a tank by mainstream fish-keepers. They work by pulling water up through an intake tube that hangs into your tank. The water then fills up a box-like reservoir that is filled with filtering material. This material is usually a block of coarse sponge, activated carbon, and some ceramic biological stones. In some cases the coarse sponge element and the carbon are combined into a cartridge. The biological element in cases like these is usually handled via a fiber-like wheel often called a “bio-wheel”. In cheaper power filters, the biological element is just a black coarse sponge, and in still other cases, there is no biological filter at all. These filters that lack biological filtration should be avoided. Power filters can be used for any aquarium set-up provided that the intake strainer cannot suck in baby fish or shrimps. Often you can add a protective “pre-filter” foam sleeve to prevent this. Power filters are generally not chosen for tanks larger than 90 gallons due to their somewhat limited biological filtration. They are also generally not the number one choice for planted tanks as they can be somewhat bulky looking aesthetically and the waterfall effect that they employ can remove Co2 from your aquarium if you allow your water level to drop from evaporation or otherwise. This by-product is a point of some debate by aquarists as some would argue that the amount of C02 they remove is minimal and not worth being concerned with, others would say that any amount of wasted Co2 is a problem worth preventing.
Advantages - Power filters are quite customizable. They are really just a place outside of your aquarium to put filtration media and have water moving through it. They are ideal for tanks under 90 gallons where the livestock load is moderate to low and where Co2 is not needed or relied on for plant growth.
Drawbacks - Power Filters can suck fry and shrimp into them. They also have the issue of “bypass” if the filter material is not kept clean. The limited surface area for biological media is not suited for large aquariums over 90 gallons and the breakage of the surface of the water makes them second fiddle to the canister filter for planted aquariums.
Who should use them? At some point in your fish keeping life, you are bound to use a power filter of some kind. If you have a tank under 90 gallons with livestock that is not too demanding with regard to waste processing, a power filter may be perfect for you.
Sponge Filters - These simple, easy filters are similar to an under-gravel (UG) filter, which we will discuss below, in that they utilize a slight current that an air pump generates by forcing air through a rigid tube. This tube is much smaller than that of an UG filter and the sponge filter is generally no bigger than a large can of soup. These are still very popular with breeders of fish and shrimp as the fry cannot be sucked into the filter in any way. They provide a gentle source of biological and some mechanical filtration. Sponge filters also get clogged fairly fast and need to be cleaned regularly in order to keep them working properly. Great for quarantine tanks, hospital tanks, shrimp tanks, and any time you are breeding fish. Not the best choice for a main filter in your show tank.
Advantages - For hospital and breeding tanks, there is likely no better choice. They cannot suck fry into them and provide heavily oxygenated water to the inhabitants.
Drawbacks - Sponge filters can clog easily if your tanks waste levels are somewhat high. They then need to be cleaned which removes most of the bacteria you spent time building up. Often a solution to this problem is to use two side by side, which allows you to clean one at a time thus keeping ample biological bacteria at work in your tank. They have a similar drawback to keeping live plants in tanks as UG filters in that they remove valuable Co2 from the aquarium.
Who should use them? Breeders of shrimp or fish, hobbyists who quarantine their newly acquired livestock, or hobbyists who are medicating fish in a hospital tank.
Internal filters - These filters are popular in aquarium kits sold at chain stores. They are cheap to produce, and are simple to use. They are also famously hideous to look at as they go in the water and are hard to hide. Additionally not very effective biologically as the water traveling through them is generally slow moving with very little oxygen involved. Most utilize a ridiculously cheap piece of coarse sponge as a biological element. This wouldn’t be the end of the world if the tank owner knows what they are doing and does not overload the tank, never overfeeds, and does frequent small water changes. The problem is that most people that buy aquarium kits are just starting their journey into keeping fish. These are the people that should be able to rely on a good filter even more so than the few of us that have been doing this for a while so unfortunately 99% of these internal filters are kind of like starting out with one foot in a hole. We say 99% because there is always an exception. There are amazing internal filters out there, just not ones that usually come in kits. As a rule, we don’t recommend these filters but don’t rule them out completely as some of the good ones are worthwhile.
Advantages - There are times when space outside the tank is limited. If a power filter cannot be used due to space restrictions and a canister filter is out of the question due to space or cost, you may find that this style of filter works for you.
Drawbacks - Internal filters are usually not the choice for someone who needs heavy filtration as they are only designed for light duty. There are some models that are customizable and feature additional media chambers thus making the filter able to compete with some of the nicer power filters, but these are few and far between. They are not the best choice if a good colony of biological bacteria is needed as they usually lack the surface area needed for this. They are also usually unsightly as they need to be in the tank where you will see them. Lastly they take up precious real estate from the fish and plants.
Who should use them? People with limited space. They also employ a lower draw and will not usually be a problem with small shrimp or fish fry. They are popular in terrariums or aquariums with limited water in them as they can sit in as little as 4” of water in most cases and work great.
Undergravel (UG) filters - This used to be the go-to method for filtration. UG filters ruled the hobby at one point. They were cheap, easy to install, and did the job. They work by directing air, via an air-pump, into the tank through a rigid tube. This tube is connected to a plastic plate that runs the length of your aquarium underneath the gravel bed. The plate is raised so that gravel sits on top of it leaving the underside of plate open to allow for water to flow. The air being forced through the rigid tube then creates a slight current slowly drawing the water, along with debris, down to the gravel bed. The gravel then becomes the sole source of mechanical filtration and, more importantly, the biological element of your tank. You can make your UG filter even stronger by replacing the air pump’s air delivery system with powerheads. You then have motors driving the current through the gravel bed, increasing your flow rate and therefore filtration. UG filters require that your gravel bed be kept clean enough to keep it from clogging the filter plate below the gravel, but dirty enough to keep the biological bacteria that lives in the gravel alive. Some people started incorporating power filters along with the UG filters which then give them a true source of mechanical filtration, some chemical filtration from the carbon in the power filter, and the biological filtration from the UG filter. They have limited capability when it comes to mechanical and chemical filtration. They are also ugly. You have at least two and in some cases up to 4 rigid 1” tubes running from top to bottom of your tank that can get covered in algae and require frequent cleaning if you want them to look decent. Add the powerhead option which makes them work better, and they become even more of an eye sore. Also, they are less than optimal for keeping live plants. The roots of the plants bind and clog the filter plate over time and the air curtain that makes them effective flushes Co2 from the tank.
Advantages - Used correctly, UG filters are biological bacteria playgrounds. This can go a long way in keeping your tank clean, clear and healthy. The use of powerheads in place of the standard UG filter cartridges make the filter very effective in moving a greater amount of gallons per hour through the filter plates.
Drawbacks - UG filters are only as good as the gravel bed. Using too little gravel doesn’t allow for full advantage to be taken with building up helpful bacteria. Using too much gravel keeps the gravel bed from being as oxygenated as it could be, building harmful bacteria if it is not clean enough. Clean the gravel too well, and you remove the helpful bacteria that is the whole point of the filter in the first place. They are visually unattractive and are not good for planted tanks as the roots of the plants can bind the filter plates over time.
Who should use them? - Even though the UG filter is becoming the dinosaur of the industry and they are somewhat hard to find, they are a great choice for the basic community tank that doesn’t require heavy filtration. They are also ideal for breeding tanks as there is no filter to suck fry into.