# How many filters do I need?



## JET (Dec 20, 2008)

I have been reading lots of posts of people with 2 filter systems. My new tank is 72g bowfront, just starting to gather up stuff for it. I bought an eheim 2217 for it. Why would so many people need two? Did I buy too small of a filter for this size tank? Should I buy another one?


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## Zapins (Jul 28, 2004)

People like a few filters because it improves circulation around the tank, preventing certain areas from experiencing no water movement. Filters in planted aquariums only help move the water around, they don't help much with cleaning the tank like in a fish-only aquarium.

The eheim 2217 will be fine for your tank.


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## JET (Dec 20, 2008)

There will some fish, small schooling type and maybe some shrimp.


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## Quetzalcoatl (Feb 13, 2009)

Filter size should be determined by your fish load, not so much by tank size.
If you have a small tank but many fish, you need bigger filter. If you have a large tank but very few fish, then you don't need too big of a filter. 

There are various reasons why people may use multiple filters. One was already mentioned by Zapins. I use two filters in-line, meaning output of my first filter is connected to the input of the second filter. The reason I do this is so that I can leave my second filter which only has bio layer untouch for very long time. 
I also have Aqua Clear, one that hangs on the tank top. This one I use for temporary/emergency cases. It is nice to use since it is so easy to place it, clean it, and remove it.


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## supersmirky (Oct 22, 2008)

Quetzalcoatl said:


> There are various reasons why people may use multiple filters. One was already mentioned by Zapins. I use two filters in-line, meaning output of my first filter is connected to the input of the second filter. The reason I do this is so that I can leave my second filter which only has bio layer untouch for very long time.
> I also have Aqua Clear, one that hangs on the tank top. This one I use for temporary/emergency cases. It is nice to use since it is so easy to place it, clean it, and remove it.


Q - This lost me. You have two filters connected to each other so the tank basically only has 1 input and 1 output?


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## Quetzalcoatl (Feb 13, 2009)

supersmirky said:


> Q - This lost me. You have two filters connected to each other so the tank basically only has 1 input and 1 output?


Correct. Water from tank enters the first filter, output of the first filter connects to the input of the second filter, output of the second filter returns to the tank. Only need to run the motor on the second filter.


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## JET (Dec 20, 2008)

Quetzalcoatl said:


> Correct. Water from tank enters the first filter, output of the first filter connects to the input of the second filter, output of the second filter returns to the tank. Only need to run the motor on the second filter.


Wow, isn't that pretty tough on that single pump motor dragging the water through two filters? Seems like that would heat up the motor. I like the idea, what kind of filters are you using?


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## BryceM (Nov 6, 2005)

Centrifugal pumps (everything we use) aren't really affected by the particulars of their connections. As long as there is at least some water movement to help with cooling and as long as they don't cavitate, they'll do their job just fine.

Using only a sinlge motor would be expected to reduce total flow rates, but the pump itself doesn't notice. It turns at a constant speed and uses about the same amount of energy no matter what it's asked to do.


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## Quetzalcoatl (Feb 13, 2009)

Pump isn't really pushing or pulling water through the filter. All it does is push the water back up into the tank. The majority of work of pushing water throught the filter media and foam into the pump is done by gravity. Since our canister filter is below the tank, by siphon effect water will naturally drop into the canister.

BTW I have fluval 304 and 204


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## intothenew (Aug 1, 2008)

I use two, one canister and one HOB, in a 55g. 

The canister is for the heavy work, lots of area for mechanical and bio filtration. It is also less apt to bypass.

I use an HOB(hang on back) for extra water circulation and to dose in. I feel that dosing anything in it helps dilute it before the tank. I also keep a pack of Purigen in it where it is easily seen for color change. It also allows water samples to be pulled without moving the lights or hood.


Convenience and utility.


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## steffish (Feb 22, 2009)

Once New Tank Syndrome-"I really need to start ANOTHER new tank!" Kicks in, you have a cycled filter ready to go!


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