What is the best aquarium filter?

Aquarium filters are vital life support systems for aquarium fish. Without filters, and the beneficial bacteria inside them, we would not be able to keep fish as their tanks would pollute and they would poison themselves with their own waste. Filters come in all shapes and sizes and there is one to suit every tank size and budget. But which one is best? 

The basics

Every filter needs to clear water and convert toxic ammonia into less harmful substances. Trapping waste is called mechanical filtration and converting waste using bacteria is called biological filtration. If you want to absorb something from the water or alter it, that’s called chemical filtration.

The best filters will combine mechanical, biological and chemical filtration, but simple foam filters can mechanically and biologically filter using just a sponge. You need small filters for small tanks and big filters for big tanks and big messy fish. The larger the filter output and media volume, the larger the tank it can filter and the more fish it can support.

Internal filters are the easiest

Internal filters go inside the tank and can be air powered by an airpump or water powdered by a powerhead or pump. They are simple to use and install, small, so good for small tanks, and cheap to run. Air-powered sponge filters are necessary for tanks containing fish fry as they use very gentle filtration and won’t suck up the baby fish. Internal power filters create a jet of water and suck in more waste, and are the biggest selling type of filter.

Basic ones contain just one sponge, but the best ones have two sponges for alternate cleaning, space to put some chemical media like carbon, and even an extra, biological section for separate bio-media like ceramics. The icing on the canister filter cake is a venturi device, which blows tiny bubbles into the water at the same time that water is pumped, providing extra aeration. 

Choose a small internal power filter for a nano tank and the largest model for large aquariums, or double up and have one internal power filter at each end of the tank. You can alternate cleaning then too, to keep beneficial bacteria levels high, and enabling them to work properly. 

new Eheim 5e external filter
External filters are the best choice for large tanks and messy fish

Use external filters for large aquaria

External filters are large canister filters which sit inside the cabinet underneath the tank. They combine mechanical, biological and chemical media for all-round, powerful filtration. They are best for large tanks and large fish, but can also be doubled-up for extra-large or extra messy situations. They are more complicated to set up than internal filters and have the potential to leak if installed incorrectly. But do it right and you’ll have no leak problems and peace of mind. Millions are used all over the world. 

So which aquarium filter is best?

Just like cars, filters come in all shapes and sizes to do different jobs, in different applications. If you want cheap, small and simple, opt for an internal power filter. If you want dirt busting capabilities and strong water flow go for an external. But as good as any new filter is, it’s sterile when you buy it and will need to be matured with beneficial bacteria before being capable of supporting fish. Mature all new tanks and filters and test water for pH, ammonia, nitrite and nitrate.   

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Jeremy Gay is an author, lifelong fishkeeper, and aquatic specialist. He's a former editor of Practical Fishkeeping Magazine, UK editor at Reefbuilders, a former aquatic store manager, and has collected fish in Sri Lanka and the Amazon. He's been on tv and radio, contributed to Koi Carp and Gardeners World magazines, been a product tester, a judge, and a product developer. Jeremy is here to guide and advise you on all things tropical, pond and marine, from set-up to stocking, health, feeding to breeding, as well as solving many common fishkeeping problems along the way.

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