On a picture in the German Wikipedia article of a mat/Hamburg filter I see a gravel blockage (plastic piece at the bottom of the fixation glued to the ground) and was wondering about its purpose:

enter image description here (see https://de.wikipedia.org/wiki/Datei:Eck-HMF.png for license)

I don't find a notion of it in the article or any of the referenced websites.

I can't image anything going past the mat no matter whether there's the blockage or not.

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    I could ask on de.wikipedia, but discussion on Wikipedia are rather painful and inefficient. Jun 28, 2016 at 13:27
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    I it just a way to filter your water, normally the sponge is in your filter, in this solution it is in the aquarium itself. The water will go trhu it, but the debri won't so it will filter the water.
    – M.P.
    Jul 6, 2016 at 14:55
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    But it does that without the gravel blockage as well. Seems like you're describing how the filter works and not referrring to the gravel blockage. Jul 14, 2016 at 16:42

1 Answer 1


It's just to prevent gravel from sliding into the corner when the filter is removed for maintenance or to be replaced. Without it, a person would typically need to use both hands when changing the filter, 1 to pull and hold the gravel out of the corner, and the other to insert the filter.

As far as filtration functionality goes, it's irrelevant, it's just there to keep the gravel from interfering with installing the filter sponge.

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