Different Types of Aquarium Filters: How They Work and Choosing the Best One for Your Tank

How to treat fin rot

Fish health depends on a good tank filter. Photo by Carnat Joel/Flickr


There are several different types of aquarium filters to provide clean water to keep angelfish and their tankmates happy. Which aquarium filter you choose will depend on your tank size, number of fish, and personal preferences. You can also combine types of aquarium filters for a clean tank. Whatever aquarium filter you use, it should be part of a regular aquarium maintenance plan.

How Aquarium Filters Work

The three ways to filter an aquarium are mechanical, biological and chemical. Most aquarium filters normally incorporate more than one system.

Mechanical systems pass water through a filter media such as foam or wool to trap particles and keep water clean.

Biological filtration encourages bacteria growth to decompose ammonia and other harmful chemicals. Bacteria attaches itself to anything and will grow on any surface of the tank such as stones, gravel and foam in the mechanical filter. Ceramic rings and bio balls are included in some biological filter systems for bacteria growth.

The chemical method uses materials such as carbon or zeolite to remove harmful substances. Zeolite can’t be used continuously as it kills bacteria. Carbon is used with most of these types to help reduce odors. When deciding on a filter it’s a good idea to get one that is rated for more capacity than what’s recommended for your tank.

Internal Fish Tank Filters

Internal filters are used inside the aquarium. They can be a simple plastic box with carbon and foam or wool to provide mechanical and biological filtration. It also uses air to draw water through the filter media then bubble through the water. Internal power and multistage are the best internal filters, but they are bigger and more complicated. A power head on the filter draws water through the filter material and cleans the water. These filters do the three kinds of filtration. The powerhead method moves more water through the filter than air powered devices.

Canister filters such as this one found on Amazon are best for large tanks.

External Aquarium Filters

External filters provide high water turnover and can handle large solid particles. External filters come in big enough sizes to handle the biggest aquariums. The typical operation for this type of filter is for a pump to pull water from the aquarium, through layers of filter media, and pour it back into the tank, which also provides aeration.

External filters are generally in canister or box form. Canisters are round or square and can be hung on the back of the tank, or put on the floor. Canister filters are generally for bigger tanks.

The box type filter is hung on the back of the aquarium and generally contains charcoal and a sponge or other filter medium. These are called hang on the back (hob) filters. External filters, such as this one, are easier to maintain and clean than internal filters.

Diatomaceous Earth Fish Tank Filter

Some users consider this type of filter the best ever made. They filter particles 0.8 to 1 micron which is small enough to remove ich, parasites and algae. It removes small enough particles it can be used to control some diseases. Diatomaceous earth is a finely powdered sedimentary rock used as the filter media in diatom aquarium filters. This filter is to be for occasional use as it will filter out and kill bacteria and an alternative to medication for some ailments. This filter makes water crystal clear.

Types of aquarium filters

Undergravel fish tank filters like this one filter water from the bottom of the tank. These are best used in tanks with artificial plans.


Undergravel Fish Tank Filters

Undergravel filters were popular several years ago, but aren’t effective when used as a primary aquarium filter. Undergravel filters are slotted plastic plates with air uplift tubes on the aquarium bottom and covered with substrate. Plate sizes are specific to the aquarium size. The best models have larger diameter uplift tubes, and wavy plates which provide more surface area. Undergravel filters are strictly a biological system. They encourage bacteria grow in the gravel and decompose ammonia. Air stones in the tubes draw water through the gravel to make the system work. Powerheads increase the volume of water moving through the gravel.

Plants don’t grow well with undergravel filters, particularly with powerheads as water flow through the gravel inhibits plant growth. Undergravel filters aren’t effective with the fine substrate plants like as the debris will clog the gravel. The best recommendation for undergravel filters is to use them in conjunction with an outside filter. Undergravel filters shouldn’t be used alone, but in addition to a mechanical filter.

Whichever filtration system you choose, aquarium filters should be part of a complete maintenance program. Water changes and other tank maintenance should be a regular scheduled program which includes filter maintenance.

This entry was posted in Angelfish Care. Bookmark the permalink.