# biological filter question



## americanthighs (Feb 16, 2011)

Hey everyone,

I'm confused as to what a "biological filter" actually is. I've done some research online, and some describe a "bio filter" simply as the bacteria that live in your tank, and others describe actual filter media that you put into your filter.

In my 10 gal, it came with a little rough-looking sponge-y thing that I placed in front of the regular filter cartridge, but my new 40 gal did not and I can't find anything that is made for my particular filter (Top Fin 40 Power Filter using Bio-bag filter cartridges).

I read that a bio-filter could be made from any inert sort of media, the greater the surface area, the better. I've seen little nylon bags being sold in PetCo that are used for Fluval filters - could I use one of those and fill it with some kind of media (the less expensive the better)? What could I fill it with? Or do I even have to worry about it? I'd think a place for the bacteria to colonize would be pretty important since I throw out the filter cartridges every couple of weeks.

Thanks guys.


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## jrman83 (Jul 9, 2010)

Your bio-filter is basically your beneficial bacteria. Formed initially when the tank is cyclng. The filter that pumps water is your mechanical filter. Parts of it support the bio-filter as it has places for the bacteria to colonize.....sometimes referred to as bio-filter media.


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## americanthighs (Feb 16, 2011)

jrman83 said:


> Your bio-filter is basically your beneficial bacteria. Formed initially when the tank is cyclng. The filter that pumps water is your mechanical filter. Parts of it support the bio-filter as it has places for the bacteria to colonize.....sometimes referred to as bio-filter media.


right, i understand that - i guess my main question is since my mechanical filter didn't come with a bio filter (my 10 gal came with a spongey-looking one), could I make one and place it in my mechanical filter?


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## jrman83 (Jul 9, 2010)

Yes you can. A lot of people prefer to make their own filter media. 

What type of filter is it - brand?


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## americanthighs (Feb 16, 2011)

jrman83 said:


> Yes you can. A lot of people prefer to make their own filter media.
> 
> What type of filter is it - brand?



Top Fin Power 40 Gal Filter, which uses standard large filter cartridges.

There's enough space between the back of the filter and where the water comes out into the tank to fit something, which is where the bio filter was located on my other tank. about 4 inches wide, and maybe an inch, inch and a half of space to fit something in.


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## Dean715 (Feb 3, 2011)

Ive never used a Topfin. When I had larger tanks I always used the Aquaclear power filters. What I used was the sponge/insert that came with the filter but instead of the carbon bag I just put filter floss on top of the sponge. I also put a mesh bag with biomax on top of the floss. I dont know that it was needed but it sure didnt hurt and helped hold the floss in place until it settled in. I would changed the floss now and then and rinse the biomax and sponge in water I had siphoned off when it seemed needed. The carbon inserts are an option but I found the floss to polish the water quite well.


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## majerah1 (Oct 29, 2010)

You sure could!Also,if you have the room you can add ceramic discs to the filter behind the pad.I saw a power filter someone has where it had the ceramic rings in the bottom with a fine filter floss pad on top of it.It could work,and I think it would be a better filter.The carbon in the pads is for odor control and to keep the water clear.If you dont have driftwood or you do your water changes,then really carbon isnt neede all the time.


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## PolymerTim (Sep 22, 2009)

If you're looking for cheap, I would just start with a little extra filter floss. You can get a bag of it at your local fish shop pretty cheap and cut to fit the space behind your filter cartridge.

I am curious why you have to change your filters every two weeks? Unless there's a specific reason, generally, you shouldn't need to change them that often. In fact, I'm still running one from about a year ago. I just wash it in used tank water and stick it back in. Definitely gives me more peace of mind for the biological filter.

For my thoughts, the biological filter is the combination of the beneficial bacteria and whatever mechanism you use to pass water over it. The bacteria will colonize every surface, including your gravel and tank glass, but the power filter will help it function by circulating the water over it to be cleaned. I think this is why some people refer to equipment (such as a biowheel) as a biological filter, even though it will only function as such once colonized with bacteria.


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