External Fish Tank Filtering Systems

Which is better for a tropical aquarium, an external filter system, or an internal filter system?

I am thinking of changing my 60ltr tank to a 120ltr tank. At the moment I have an internal canister type filter, but I find it distrubs my fish when I have to take it out to clean. Also snails lay a lot of eggs around the filter parts. Would an external filter cause less distrubance and would their be benifits to using one.

Definately an external filter. This is because they have a large area of biomedia (often ceramic media such as white ‘tubes’ called biomax or similar) which is where the beneficial bacteria can live and function efficiently. Most internal filters have just a sponge, which only provides ‘mechanical’ filtration, ie all the lumps of muck get stuck in the sponge. Trouble with this is that any bacteria in the filter have only got the sponge to live on and when this gets all clogged up with muck (in about 5-7 days) they cannot get enough oxygen to work correctly. This is why you should clean an internal filter about once a week (and only clean the sponge in dirty tank water and not under the tap).
In an external filter, you still get sponges which collect most of the large lumps of muck, but you also get other types of filter media such as chemical and biological to provide more efficient filtration.
You often get carbon in the filter, but I would replace this with extra biomedia. This is because carbon needs to be changed every month. It is useful for clearing cloudy water in new tank set-ups and also for removing chemicals such as disease treatments after a period of medication, but otherwise the space would be better used filled with extra biomax or similar. The larger area of biological filtration, the more efficient your filter will be. A tank with an external filter needs cleaning about once a month, at which time you should also clean the filter media with dirty tank water and not tap water. Good luck!

Incidentally…have you tested your tank water for nitrates? Only because you mentioned snails and these often are a sympton of poor water quality. You may wish to get a fish that eats snails to keep the population down – for your tank size I suggest 2 or 3 zebra loaches (botia striata) will do the job. (Clown loaches do the same job, but will get too big for your tank).

Planted fish tank with external filter.

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