# undergravel filter



## dd123456 (Dec 17, 2009)

this might be a dumb question but what does a under gravel filter do ive always used one just never really fig out wat they do


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## Bert H (Mar 2, 2004)

They act as both a biological filter harboring lots of bacteria for the tank, and a mechanical filter by removing things from the water column. Gravel vacs are very important in an undergravel filter, imo. They are also not the best choice for planted tanks.


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## Seattle_Aquarist (Mar 7, 2008)

Hi dd123456,

First of all I see you are new to APC.....Welcome! This is a great site with excellent information and friendly people to help you if you need it. Glad you joined us!

Bert H is correct, undergravel filters (UGF) are not typically used in planted aquariums. Most planted tank enthusiasts use canister filters as their first choice and hang on the back (HOB) filters as a distant second.

That said, I too am "old school" and use UGF in my two larger aquariums in conjunction with canister filters. I run the UGF at a low rate of flow. I like the fact that the water is drawn through the substrate (gravel) and I do not get areas where hydrogen sulfide gas can build up. It is hard to aquascape around the large uplift tubes however! LOL I know that the increased circulation and surface agitation is probably causing higher CO2 use and the nitrate eating bacteria that thrive in the gravel use up my KNO3 at a faster rate but my plants grow great. 

If you want to use them go ahead, just keep in mind you may have to compensate for the above negatives. Glad you are here!


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## dd123456 (Dec 17, 2009)

well thanxs never knew all that i keep that in mind, yea i use co2 system, i didnt start using that till like a month ago i didnt know bout it but yea my plant are doing 10x better now


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