# [Wet Thumb Forum]-fluval 404 enough for a 75?



## Plant idot... (Jul 6, 2003)

Do you think a single fluval 404 would be enough flitration for a 75gal? Too much?


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## Plant idot... (Jul 6, 2003)

Do you think a single fluval 404 would be enough flitration for a 75gal? Too much?


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## Hawkeye (Aug 20, 2004)

It should be OK. On my 75gal I use two 303. I like to turn over water several time an hour and keep a good water flow. All so I run a external reactor 1000 on one. That cuts down on the flow a little. 

Hawk


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## EDGE (Feb 28, 2004)

404 with external reactor will not provide enough flow rate for a 75G. I added a powerhead 201 to it and still considering adding another to increase the flowrate.


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## Plant idot... (Jul 6, 2003)

What about an eheim 2028 which is rated for a 150?


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## nino (Oct 2, 2004)

Eheim 2028 has less gph than 404.


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## Plant idot... (Jul 6, 2003)

So why woudl something rated for twice as much not be enough? I believe you but I dont know the science behind it.

And when you say added a power head to it, do you mean physicaly to the filter? How do you do that? I have never done that obviously...


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## nino (Oct 2, 2004)

I was confused before also why Eheim recommend such a big tank for their low flow rates. Then I read an article (can't recall where, it was few years ago) regarding bio-filtration by canister filters. Eheim is very particular in maximizing the bio filtration. You can see their different kinds of bio medias. If I remember correctly, the max. bio filtration efficiency is only can be reached if the gph is between 2-3.5 times the tanks size. Anything over that is more mechanically efficient but not biologically. Anything under 1.5 times is useless for bio-filtration. 

I use additional powerhead just to increase water circulation. A long tank might have some dead spot where the filter can't reach.


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## anonapersona (Mar 11, 2004)

Hmm, that doesn't seem right to me, I think the low flow rates are not based on the tank volume but the canister volume. If you look way back to the first discussion of the Mattenfilter that was here on AB, there was some info either posted or linked that had some calculation of the flow rate per cross sectional area of media. 

That makes more sense, that the flow rate ought to be linked to the rate at which bacteria can munch through ammonia and nitrite, which would require a certain contact time. So, the velocity through the media would be at some ideal rate. Once you have that, you'd size the pump speed to the cross sectional area to have that ideal velocity. then, the depth of the canister gives you the volume which ought to be linked to the volume of the tank. So, you could have a canister that has the same cross sectional area run by the same pump(at that ideal velocity), but a larger volume (with a taller canister) that would be sized for a larger tank.

If you just look at turnover of tank volume, you are skipping the actual flow rate through the media, the true contact of water to bacteria. Dwell time ought to be really important for biological filtration. If you have less media, you'd need more turnovers to get all the tank water contacted by it for the required actual contact time -- if you need to run through 10 inches of media you can either run through 10 inches of media one time or 1 inch of media 10 times. So, a HOB filter that has a bag with practically no cross sectional area would need to have a much higher turnover of tank volume in order to get the same degree of biological filtration.


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## nino (Oct 2, 2004)

Anonapersona, your explanation actually makes more sense to me than that article. I'm not saying that the author is wrong. He might base it on something else that I didn't catch correctly. But personally, I use my canisters more to clean and polish the water (mechanical) and creating water movement. If I want to be serious on biological, I would use a trickle filter.


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## Plant idot... (Jul 6, 2003)

Can someone explain to me what exactly a powerhead is and what you mean by adding it to it? Are we talking about adding a "wpoerhead" to an existing filer or is this a standalone device and when you say adding to you are referring to the aquarium as a whole?


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## anonapersona (Mar 11, 2004)

The powerhead is just added to the tank to improve circulation, you can search online at BigAlsOnline.com or DrsFosterSmith.com to see what they look like. 

If the filter has an ouput on the far side of the tank, the other side may be nearly stagnant, especially if you have thick plant cover blocking the flow. So you might want to add some circulation on the other side. A lot of us add second filters, but really it is the circulation and mechanical filtration we are looking for.


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