Aquarium Filter Types
There are many different types of filters on the market, and each have their own pros and cons. Here is some basic information on the different types of filters to help you pick the right one for your situation.
Hang On Back (HOB) aka Power Filters
This is one of the most common filter options for smaller aquariums. They are cheap, easy to setup, and easy to maintain, making them a popular choice among beginners. They simply hang on the back of the aquarium, pulling water up through a snorkel inside the tank, forcing it through the filter media - generally a proprietary filter cartridge, then dumping it back into the tank.
Internal Power Filters
These work in a similar fashion to hang on back filters, but they are submerged in the tank. They are cheap and relatively easy to setup, but they eat up valuable tank space and can be messy to clean.
These are a blast from the past, and really are not recommended. It's a big grid under the gravel, and suction created by an air pump outside the tank pulls waste down into the gravel, using the natural bacteria for a biological filtration. The problem is, it's also pulling fish waste and uneaten food down into the gravel to rot.
Air Driven Internal Filters
These are typically used for very small tanks, sick tanks and breeding tanks, because they are very cheap and easy to set up. They offer quick and easy mechanical, chemical and biological
filtration and are powered by a cheap air pump outside the aquarium.
These are excellent for large aquariums, as they can process a ton of water, hold a a lot of filter media and have a lot of options for flow and output. The water is pumped up and out of the tank, down a hose into the canister. The canister typically has several layers of filtration media, allowing you to use different types of filtration to custom tailor it to your needs. Most canister filters also include several methods of putting the water back in the aquarium, from a simple faucet style hose, to a spread faucet that spreads the water out more, and even spray bars that simulate a rain like effect all across the tank, maximizing the oxygenation of the water.
Wet / Dry Filters
These are the most efficient biological filters, keeping the media exposed to both oxygen and water at all times. They also maximize the surface area, allowing enormous amounts of beneficial bacteria to live and process the dirty water.