An aquarium filter is one of those absolutely required fish tank equipment to run a home aquarium without fish dropping like flies. A fish will not survive for long in a fish tank without an aquarium filter system running 24/7. To make the point clearer, please do not get any pet fish at all if you do not plan to install an aquarium filter.
What is an aquarium filter for? Why do we need it?
There are three primary functions for an aquarium filter system in a fish tank.
1. Biological filtration
The most important and absolutely necessary function of an aquarium filter system is for biological filtration. To sum it up, biological filtration in an aquarium is the process of converting the toxic ammonia produced by fish to relatively harmless nitrate. Without biological filtration, no fish can survive in a closed system such as in a home aquarium for long. To understand it further, you must first understand Aquarium Nitrogen Cycle which is one of the most important knowledge every fish hobbyist must learn.
2. Mechanical filtration
Mechanical filtration is to remove debris such as fish waste, leftover fish food, and other debris from the fish tank water.
3. Chemical filtration
Depending on what filter media you have in your filter, aquarium filters with activated carbon pads are capable of removing certain dissolved chemicals from the water.
Contrary to the common belief, the primary function of an aquarium filter system is not for the traditional sense of “cleaning.” Although mechanical filtration is part of the functions of many types of aquarium filters, the main function of an aquarium filter is (not) to get rid of fish waste or other debris in the tank water. The reason is simple, even if the aquarium filter has removed the debris such as fish poop and leftover fish food, it really has only removed it from your sight. The fish waste and fish food inside the filter is still polluting the water of the tank since the water is cycling through it every second. Thus, it is pointless to depend on the aquarium filter to remove fish waste and other debris from your fish tank. On a side note: To truly remove the debris from your fish tank, you should use an aquarium vacuum.
Chemical filtration is often used to remove bad smell from the fish tank water. However, any well maintained healthy aquarium should not have bad smell at all to begin with. Activated carbon can’t absorb unlimited amount of chemicals, thus it is only a temporary fix rather than a sustainable solution. As the matter of fact, most experienced fish hobbyists do not use activated carbon pads at all in their aquarium filters, because it serves no purpose unless they want to remove medication from the water column in the case when they have just treated the fish for certain diseases or parasites.
That leaves only biological filtration as the main purpose of the aquarium filter system. Without it, fish will die due to ammonia poisoning. Once again, if you have not read the article of Aquarium Nitrogen Cycle, we highly recommend that you read it in order to get a full understanding on biological filtration in an aquarium.
Important Note: Since all fish produce ammonia on a constant basis, the aquarium filter system must be running at all times to keep ammonia at zero. Daily water change is no substitute for an aquarium filter system. You will still need a filter even if you do water change multiple times a day. Do not skip the filter system when you set up a fish tank, and never turn the filter off when you have fish (aside the little time you spend on fish tank maintenance). An aquarium filter is as important as the fish tank itself. Neither should be there without the other one.
Now you know the importance of an aquarium filter system for a fish tank. There are so many different types of aquarium filters out there. Which filter should you use? To choose a filter system, you must first understand the different types of filter systems.
Different Types of Aquarium Filters:
1. Power Filters
These filters are often hanging on the back of the fish tank, and creating a waterfall as the water is filtered and thrown back into the tank. They are fairly cheap, and they are the most commonly used filters for this very reason. They also have down sides, which include the noises (waterfall, as well as the motor). The intake and outflow of most power filters are fairly close to each other, which makes the intake continue to take in a lot of water which was just filtered. Power filters also have limited filter media, which makes biological filtration a less strong point. While it might be a good choice for small- to medium-sized fish tanks, personally I would not recommend a power filter for anything more than a 30 gallon (or 110~120L) tank that is heavily stocked with a lot of fish. You may however use two or more power filters for a single large fish tank, but it defeats the strong point of being cheap. AquaClear power filter is one of the best power filters available.
2. Internal Filters
Internal filters are placed under the water in a fish tank, thus they are also called Underwater Filters. They take space inside the tank. While they do fine for both biological and physical filtration, they are usually made for small- to medium-sized fish tanks.
3. Canister Filters
This is the very high end of aquarium filter system. They appear to be in the form of a large canister. The whole filter is usually located below the fish tank, with only its intake and outflow tubes visible inside the tank. Canister filters are extremely quiet. For example, I have an EHEIM Classic 2213 Canister Filter, and I can’t even hear anything at all without putting my ear directly against it. Canister filters also hold large amount of filter media, which means they are the most efficient filters for biological filtration. By placing the intake and the outflow tubes on the opposite sides of the tank, it solved the issue of the weakness of a typical power filter.
Canister filters are highly efficient, but they are not cheap. There is no need to get one unless your tank is at least 30~40 gallon (110~150L). I might be biased. This is my favorite type of filter system because of its high efficiency and 0 noise level.
4. Wet/Dry Filters
This is another high end form of aquarium filter system designed for large aquariums. Wet/Dry Filter is the preferred filter system for many saltwater aquarium hobbyists.
5. Sponge Filters
This type of aquarium filters is the simplest form of filters, and thus the cheapest. Unlike other filters which have their own little motor to pump the water through the filter media, you will need a water pump or air pump to power a sponge filter. Sponge filter itself is nothing more than a piece of sponge on the top of a few other parts including a tube and an air stone (although usually you have to get the air stone separately yourself).
Sponge filter can be used independently, and it can be used as pre-filter on the intake of power filter or canister filter to increase biological filtration as well as pre-filtering debris in order to decrease the maintenance requirement for other more complex filters. The sponge filter is perfect for low budget aquariums. Unlike other types of filters, a sponge filter will not suck anything into it, thus making it perfectly safe for small fish fry and shrimp. It is the ideal filter for a breeding or fish fry tank.
The negative aspects of a sponge filter are: it takes extra space inside your tank, and it might not be pretty “decoration” inside your tank.
While it is not as efficient as a canister filter, multiple large sponge filters powered by a single air pump with split valve should be good enough for even a large aquarium of any size. It is also a perfect solution for those hobbyists who run many fish tanks on a limited budget. You do not have to buy expensive filters for every one of your fish tanks. Just one cheap sponge filter per tank hooked up to one or a few air pumps will meet all your biological filtration needs.
My favorite sponge filter is Hydro Sponge Filter. Three out of four of my smaller fish tanks have them running for years without a problem. If you decide to go for sponge filters, make sure you also have an aquarium air pump, air tubing, and air stone to power it.
Which types of aquarium filter should you choose for your fish tank?
To choose an aquarium filter system, you should look at two things: The level of filtration your need for your aquarium and your available budget. Larger aquariums require better filtration. Lower budget can only afford cheaper filters. It is easy to understand.
In summary, I recommend Power Filters for aquariums no more than 30 gallons. You may also use internal filters for the same aquariums if you don’t mind the space they require in the tank. A canister filter is the best choice for anything more than 30 gallons, if you have the budget and you like its quietness and efficiency.
All aquarium filters have a set of specifications provided by the manufacturers. What you must pay attention to are two important things:
1. Recommended fish tank size
This is the tank size recommended by the manufacturer to use with their filters. Note that most of them say “up to 20 gallon” or “up to 30 gallon”. It is the maximal size of tank the manufacturers say you can use with their filter.
A heavily stocked tank with more or bigger fish definitely requires more filtration than a lightly stocked tank of the same size. This “up to” is most likely used in the case where the tank is lightly stocked. You should always go one step up on this rating unless your tank is indeed very lightly stocked.
2. GPH (or Gallon Per Hour)
This is the flow rate of the water. The faster the water goes through the aquarium filter, the more efficient the biological filtration is. If you are using a power filter, usually the recommended GPH should be high enough to go through your entire tank water 5~7 times per hour. Canister filters are on a different level because they have a lot more filter media in them, and they should be fine with just enough power to go through all of your tank water 3 times per hour.
GPH on most aquarium filters are rated with an empty filter without filter media in there. Once a filter is filled with filter media, the actual GPH should be a lot lower. One exception is EHEIM, a reputable German brand. The GPH on their filters are rated with full set of filter media. My EHEIM classic 2213 canister filter has been working in a heavily stocked 40-gallon aquarium flawlessly for years.
Whatever aquarium filter you choose for your fish tank, it should be efficient enough. Underpowered filter will not provide enough biological filtration and thus there will still be ammonia in the water, which will defeat the purpose of having a filter. With a very efficient filter doing its job, the only maintenance you need is weekly partial water change. You may install multiple filters in the same fish tank, or you may get a filter which is rated way higher than your fish tank size. You can never have too much filtration. With the exception that water current is too strong for the fish, more filtration is always better.