Aquarium Filter 101 (Function; Purpose; Types; and How to Pick one)

Aquarium filter is just as important as the fish tank for having an aquarium at home. We can’t skip either of them as long as we want to keep fish alive.  A lot of people started their first fish tank without even have a filter. It is no wonder why most fish die within the first a few weeks.

Just to be straightforward, fish will die if there is no filter in the fish tank.

To understand the importance of aquarium filters, we first must know what they do.

The Function and Purpose of an Aquarium Filter.

There are three primary functions of a filter system in an aquarium.
1. Biological Filtration
Biological filtration is the most critical function of an aquarium filter. First, we must understand what an aquarium nitrogen cycle is. The one of the most critical knowledge we must process before getting any fish. The aquarium nitrogen cycle is very much relying on the filter.

Since fish produce toxic ammonia which is harmful enough to kill them, the ammonia must constantly be kept at 0ppm. The aquarium nitrogen cycle is the only way to keep ammonia at 0ppm constantly.

Multiple species of beneficial bacteria will feed on ammonia and nitrite and convert them to the relative safe nitrate. Because these bacteria have to colonize surface areas on objects, the more surface area you have in the aquarium, the more beneficial bacteria you will have. Heck, the only place with enough surface area is the filter media inside the aquarium filter. It is the reason why we need the filter in the first place. It is to provide enough surface area for the beneficial bacteria to colonize on in order to neutralize the toxic ammonia produced by the fish.

Without constant biological filtration taking place, the fish will eventually die of ammonia poisoning in a closed system.

2. Physical filtration
Physical filtration is to have the aquarium filter physically remove the debris such as fish poop, leftover fish food, or any small and floating stuff in the water.

It is not as important as the biological filtration. Actually, we do not even need it in most cases. While some types of filter system are strong enough to suck in and filter out the debris, they do not actually remove the trash from the system. Because the aquarium water constantly goes through the filter, anything rotting inside the filter will still pollute the water. Suck in too much debris will also slow down the water flow and affect the efficiency of the filter. Also, it will increase the maintenance need.

Therefore, we do not rely on the physical filtration to remove the debris. Instead, we should use the fishnet and gravel vacuum to remove debris from the fish tank.

Many aquarium hobbyists even use a piece of sponge as pre-filter to prevent the debris to get into the filter to lower the maintenance need for the filter.

3. Chemical filtration
Some filters have the activated carbon pads inside in addition to other types of filter media. Activated carbon can absorb chemicals from the water. It is useful if you need to remove something such as fish medication from the water. Otherwise, we do not need it either.

Activated carbon has its limit. It can only absorb a finite amount of chemicals. Once it is full, it will start leaking the chemicals back into the water slowly. So even if you prefer to use carbon pads in the filter, you have to replace them every month or so. Unnecessary additional cost and labor in my opinion. Besides, it does not even remove toxic such as ammonia and nitrite.

Conclusion, we only absolutely need the biological filtration. Therefore, the priority is to find a filter good at biological filtration.

Now we know the function of an aquarium filter system.

The next step is to know which filter to pick.

Different types of Aquarium Filter Systems

There are at least six types of different aquarium filter system.
1. Power Filter
A power filter is the most used type of all aquarium filter systems. They are the type of filters which some people call “hang on the back filter”. Because they are usually hanging on the back of the fish tank. And they create a waterfall as the water come out of the outflow.

Pros: Available almost everywhere that sells aquarium stuff. Fairly cheap.  Easy to install.  Not to hard to maintain. With a power filter and its waterfall, you do not have to get an air pump.

Con: Noise from the waterfall and possibility the motor as well. Not efficient enough for large aquariums. It takes also takes space on the top of the aquarium.

Example: AquarClear Power Filter. It is one of the best power filters available. Highly recommended for a small to medium sized aquarium on a budget.

2. Canister Filter
A canister filter is usually aimed at the bigger aquariums of over 40-gallon. Because they are a lot more efficient when it comes to biological filtration. They come in the shape of a canister. The canister part usually sits somewhere below the aquarium with only the intake out outflow tubes visible.

Pros: Highly efficient biological filtration since a canister filter holds a lot more filter media which provides tons of surface area for beneficial bacteria to reside on. It is very quiet. Usually, you can’t hear anything at all without putting your ears against the canister.

Con: More expensive. The price ranged from $80 to hundreds of dollars depending on the brand and model, as well as the capacity.
Harder to install compare to a power filter. But nothing is impossible with a manual and a determined fish lover.

Harder to maintain. While the frequency of maintenance can be as long as once a month or two, to clean the canister filter require to open the canister and take out the filter media. Not that hard if you know what you are doing, but it indeed takes longer maintenance time.

Example: EHEIM Canister Filter. My favorite, since mine served me for years. Some people I know have used it for decades.

3. Sponge Filter
It is just a piece of sponge usually in the shape of a cylinder, with an open tunnel goes through in the middle. The sponge filter works when it is fully under the water. It can be powered by either an air stone or a water pump. The idea is to use the air pump or water pump to pull the water through the sponge filter, and thus starting a biological filtration.

Pro:
Cheap. It is the most affordable of all if you already have an air pump. The filter itself usually goes for only around $10 if not cheaper.
Easy to install.
Easy to maintain.

Con: Since it must be put entirely under the water, it takes space inside the fish tank.
It is not good looking. Although you can hide it behind some decorations.

Example:
Hydro Sponge Filter. I have used it in multiple fish tanks with good results. It is also great for fry and shrimp tanks since a sponge filter will not suck them in.

4. Internal Filter
Internal Filter is a type of mechanical filter which is fully submersible when doing its job. Thus, it is also called underwater filter. It is not as widely used as the other type of filters.

Pro: Easy to install. Cheap.

Con: Takes space from the fish tank.

Example: Fluval Underwater Filter.

5. Wet/Dry Filter, or Trickle Filter
A wet/dry filter is another external filter with high efficiency and high price tag. They remove the water from intake tube and let it go through filter media before it gets into a sump. The water is then sprayed back into the fish tank.

Pro: Highly efficient filtration.

Con: Very expensive.

Example: Eshopps Wet/Dry Filter

6. Diatom Filter
Technically a diatom filter not in the same category of other aquarium filters. It is only for physical filtration of special purpose. Since it can even filter out micro-sized particles, it can even remove unseen parasites from the water. A great feat to keep the widely spread fish parasites in check. Some advanced aquarium hobbyists run it for only a few hours each week and swear by it that it contributes to their parasite-free aquarium.

Pro: Excellent physical filtration for removing even parasites from the aquarium water.

Con: Expensive.
Hard to find since it is a special niche item for a limited market.

Conclusion: An aquarium filter system is required to run any home aquarium if you do not want the fish to die. Choose the right filter for your aquarium is more than just to look at the prices. All filters have the manufacturer rated “recommended fish tank size”, as well as GPH “Gallon Per Hour” on them. We want to use one level higher of recommendation by the manufacturers just to make sure the biological filtration is sufficient enough.

The more GPH, the more efficient the filter is. The more filter media, the more efficient the biological filtration is. Canister filters and wet/dry filters will always be far superior to other types of filters at the same GPH when it comes to biological filtration due to their filter media size. However, there is no need to spend that much money if your aquarium is less than 40-gallon. If the budget is not a problem, then go for it for a better experience.

You can certainly use multiple aquarium filter systems in the same aquarium at the same time. Because their filtration will add up. In a large aquarium (90-gallon or above), placing one filter on each side is an excellent way to keep the filtration run throughout the whole tank. Doing maintenance one at a time can also minimize the damage to the beneficial bacteria colony.