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Internal vs External


10 Sep 2008
I have always wondered about getting an exerternal filter but i know nothing about it. I was put off getting one last time i went in my LFS when the guy went on and on and on... poor little me standing looking very confused and he was still going on and on...

I know a fair amount about internal filters having always had them. But could some one tell me a little more about external ones. (in a slightly simple female way!) (remember simple :wideyed: :oops: )

I have 125L at the moment and i was hoping to upgrade to a 200L at some point so would deffently look at getting one for that.

Thank you for any help now and for being patient with me.


24 Nov 2007
Well obviously the main difference is that the external goes outside the tank (usually situated beneath the tank in the cabinet). It will have 2 pipes in the tank, 1 sucks the water out of the tank and down into the filter, the other returns the water to the tank from the filter.
The main advantage, other than not having the filter in the tank which can be a bit of an eyesore, is a much larger media capacity than an internal, allowing for more efficient biological filtration, as well as chemical or mechanical filtration. Externals generally have great flower as well, allowing for more efficient CO2 and nutrient distribution. A general rule for planted aquaria is to aim for a filter with sufficient flow to turn the tank volume over 10 times in an hour. Therefore for your 125L it would be advisable to aim for approximately 1200 lph
There are many brands making externals, if you have the cash buy an Eheim as they are widely regarded as the best, although the Tetratec EX filters are also very good and more reasonably priced.

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