# Substrate as a biological filter



## Seattle_Aquarist (Jun 15, 2008)

Hi IUnknown,

I see you are an 'old timer' on the forum....do you recall any threads about undergravel filters (UGFs)? Substrate can be used as a biological filter quite effectively but the roots of plants will get caught up in the filter plates of the UGFs. I currently have two tanks that have UGF.

Here is one of my first planted tanks (vintage 2008), with DIY CO2, Excel, and Seachem Comprehensive and Iron. It has a UGF covered with natural gravel and an HOB.


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## Nordic (Nov 11, 2003)

I also used to use UGFs.
I think they are best used with a power head to drive the flow.
Also, stick a wad of floss right under the hole where the bubbles normally returns to the surface. This prevents crap that made it to the tank floor from getting blasted out into the tank again.

Just an observation, I noticed with my cory tank, there is almost never any visible poop. It has maybe 5mm to 1/2 inch deep uniform sized medium small grains white sand. I think what happens is, with their nuzzling the sand all day, the excrement gets ground up, thrown into the water column and sucked up by the sponge filter. Its a little tricky, as the water may appear glass clear, but the filter needs far more regular cleaning.

I like the angel on the left, the dark top/light bottom is one of my favourite phenotypes.


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## roadmaster (Nov 5, 2009)

First few centimeter's of near any substrate will house fairly large bacterial colony.
Below first few centimeter's oxygen needed for nitrifying bacteria(aerobic) is lower so anaerobic bacteria occupy the deeper region's.
Bacteria also is found on all hard surfaces in te tank like the glass,wood,rock's,plant leaves,inside wall's of canister's or HOB filter's,inside hoses from filter's in addition to biological media housed inside the filter where oxygen rich water passes through.
Lot's of plant's make best biological filter, for they use the ammonia and nitrites and nitrates as food for growth.


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