# filtration



## fishboy85 (Apr 26, 2014)

Hi all I'm just wondering if anybody knows how filter ratings are justified for example fluval u4 very fluval 206 according to them the u4 is rated at 240 like and the 206 just 200 why is it the smaller u4 is rated higher than the 206?


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## BrendanMc (May 30, 2012)

I'm no filtration expert, but different styles of filters are rated at different gph. For example, my HOB, an Aqueon 55/75 is rated at 400 gph, but my cansiter, a Fluval 306 is rated at 303 gph. Of course, the canister provides much better filtration than the HOB so gph shouldn't be the primary factor when purchasing a filter. It's also important to note the gph is without any media.


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## pablo111 (Dec 10, 2013)

BrendanMc said:


> It's also important to note the gph is without any media.


Not always. Some companies, like EHEIM, advertise the flow rate with media.

I don't know how these companies decide what size tank these filters can support. Really, it isn't about the size of the tank, but rather the type of media being used and the amount of biomass in the tank. The same filter can process the waste of 10 large mbuna in a 90 gallon tank or in a 40 gallon tank, provided it has a high enough flow rate (GPH) to turn over the larger tank a sufficient number of times per hour.

Its just a matter of having some common sense and judging the volume and flow rate of canister you will need based on your tank size and stocking plans. There is such a thing as too much flow, for example, an FX6 on a 20 gallon would produce quite the torrent of water. Too much for a lot of the fish available in the hobby (but great for fish like hillstream loaches). You just have to use your noggin and try to make a decision from there.


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## fishboy85 (Apr 26, 2014)

Was just curious to start with I thought it was rate of flow but looking a bit further into it I noticed ehiem have an eco range with the same max gallon rating but rate of flow was much less so to me that would suggest that the eco must have something to over compensate for lack of flow but im guessing not


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## pablo111 (Dec 10, 2013)

fishboy85 said:


> Was just curious to start with I thought it was rate of flow but looking a bit further into it I noticed ehiem have an eco range with the same max gallon rating but rate of flow was much less so to me that would suggest that the eco must have something to over compensate for lack of flow but im guessing not


Which is exactly why I don't trust the manufacturer's tank size rating. An Aquaclear 70 could probably support a 125G tank with 1 guppy in it. If you had 75 guppies in there you might want to look at an FX6. 
Eheim ECO, according to an old friend who had 40 tanks (major MTS illness) and had every filter imaginable, is garbage. She said she wouldn't recommend them to her worse enemy. The lowest end Eheim I would bother with is the classic (2211/13/15/17)

To give you an idea of how much you can over filter, I had a 90 gal tank with 2 Aquaclear 110s and an Eheim 2217. If I listened to Hagen, I'd believe that 1 Aquaclear 110 could support my 90 gallon fully stocked with haps and peacocks. 
You can't over filter so much as you can over 'flow'. If there is too much current in the aquarium to the point of making the fish uncomfortable, then it's a problem. However, it's not hard to diffuse the flow from filters and reduce current.

I suggest at least doubling up on the mfg's suggested ratings. If a filter is rated for 50 gallons, get at least 2 of them for your 40 gallon tank.


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## triscuit (May 6, 2005)

Also note that pump head (the distance water has to be pushed up) is a major factor in flow rates. If your canister filter is on the floor, and your tank on a high stand, you'll get a lot less out of it than you would a hang on the back filter. Of course, canisters have to be below the water level to work properly...

Many manufacturers figure in an average pump head for the ratings, but it's worth reading the fine print when comparing price vs. output of different brands.


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## smitty814 (Sep 27, 2012)

Flow rate advertised by filter companies is dubious at best. Most companies flow rates are without media and no head. Eheim's may be with media but with no head. 
The filtration you need is whatever can keep your water parameters (ammonia, nitrate and nitrite) in check. In other words, if you have an AC 110 for example, and that keeps your ammonia at 0ppm and nitrites at 0ppm. Then that is the proper filtration for the bio load in your tank.
Without monitoring water parameters it is very easy to buy too much filtration.


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## fmueller (Jan 11, 2004)

triscuit said:


> Also note that pump head (the distance water has to be pushed up) is a major factor in flow rates. If your canister filter is on the floor, and your tank on a high stand, you'll get a lot less out of it than you would a hang on the back filter.


triscuit - are you quite sure about this? I was always under the impression that pump head has a minimal - if any - impact on the flow rate produced by canister filters. It has a huge impact when you are dealing with sump systems, because the pump in a sump actually needs to physically push the water back up to the tank. However, in a canister setup the pump is siphon fed. If you switch off the pump, the water level in the outflow pipe will still be at tank surface level. All the pump does is keep the water moving. The siphon does the work of pushing it up.

Of course if you have excessively long hoses that might reduce flow - particularly if they are dirty - but it shouldn't make a difference if a canister is 10' below a tank, or 10' beside it. At least that's the way I've always heard it


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## smitty814 (Sep 27, 2012)

The pump in the canister has to pump the water from the can to the tank. So hose length and height has a huge effect. The syphon is only on the intake side. Sorry&#8230;.I'll field this one


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## triscuit (May 6, 2005)

Oooh... you made me look it up!  It's late and I'm not explaining this well, but I can see my fluid hydraulics textbook mocking me from across the room...

My new answer (after some half-baked reading) is that yes, hydraulic head does matter even in a siphoned system, but not as much as I thought it would. Most of the flow losses in a canister are going to be due to friction, which of course increases with increased hose length. Since the intake and and output of the filter have the same water height, the pump still has to push water up (the water is in equilibrium, motionless, without the pump).

Here's a page from a Fluval owner's manual to further confuse the issue:



Basically, manufacturers have some idea of the system limitations, and so when comparing across brands it might help to see if they account for distance (if not hydraulic head) in their flow calculations.

Here's the link to the owner's manual in case the image is too hard to read: http://usa.hagen.com/File/b3378f42-51ae ... fdc858d921


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## fmueller (Jan 11, 2004)

triscuit said:


> Most of the flow losses in a canister are going to be due to friction.


That's what I thought.



triscuit said:


> Oooh... you made me look it up!  It's late and I'm not explaining this well, but I can see my fluid hydraulics textbook mocking me from across the room...


It isn't this one by any chance? D J Brasch is my late father in law, but I must admit that I've never read the book - way too much maths for my taste. So I guess the relation did not really help my understanding of fluid flow


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## fishboy85 (Apr 26, 2014)

Having a larger filter doesnt reduce nitrates though does it just houses more beneficial bacteria and needs cleaned less often? Doesnt get blocked as easy yeah


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## smitty814 (Sep 27, 2012)

Yes a larger filter doesn't reduce nitrates. Increase in bio load will increase bb. Any waste in your canister is still in your tank and should be cleaned on a regular basis.


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## BillD (May 17, 2005)

smitty814 said:


> Yes a larger filter doesn't reduce nitrates. Increase in bio load will increase bb. Any waste in your canister is still in your tank and should be cleaned on a regular basis.


Well said. The function of the filters we usually use is to produce nitrate. They are all in fact the dreaded "nitrate factory", a term often used to negatively describe under gravel filters. If your filter keeps the tank at 0 ammonia and 0 nitrite, it is sufficient. Adding more filtration will not reduce those numbers. Not cleaning a cannister for 6 months is no different than not vacuuming a tank with a UGF, for 6 months. Keeping a filter clean will slow the rise of nitrates by removing solid waste before it gets broken down.
There is far too much concern for GPH rates (which can be useful) when the important consideration is whether the filter does the job or not. Ditto for, so called, turnover rates.


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## fishboy85 (Apr 26, 2014)

Thanks thats what I needed to know


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## fishboy85 (Apr 26, 2014)

Well I finally got a canister filter and installed yesterday its basically sitting on the floor hose length 3 foot each which is within the max height but I can raise it 8" higher is it worth doing that or will it be a negligible increse in flow


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## Deeda (Oct 12, 2012)

I think you will be fine as long as you aren't too close to the max height recommendation. Which brand & model filter did you end up buying?


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## fishboy85 (Apr 26, 2014)

Im at 1.2 and its rating is 1.4 iys an all pond solutions ef1000 I know its no ehiem and the general consensus on here may not aggree but the reviews I seen on it seamed alright


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## Deeda (Oct 12, 2012)

You seem well within the suggested installation height so you're fine. Don't sweat the filter brand wars, everyone has filters that are preferred, as long as they perform as desired, it doesn't matter.


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## fishboy85 (Apr 26, 2014)

Alright cool cheers mate


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## Vincenzo (Mar 6, 2014)

triscuit said:


> Also note that pump head (the distance water has to be pushed up) is a major factor in flow rates. If your canister filter is on the floor, and your tank on a high stand, you'll get a lot less out of it than you would a hang on the back filter. Of course, canisters have to be below the water level to work properly...
> 
> Many manufacturers figure in an average pump head for the ratings, but it's worth reading the fine print when comparing price vs. output of different brands.


Head is the difference in the elevation of the water levels. In the case of a tank the water level is the same. So that potential energy is zero. What the pump has to overcome is friction losses in the filtration system, which includes filter media, and desired flow rate.


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## Vincenzo (Mar 6, 2014)

Looks like everyone already addressed this. I was a little late. but one more addage. Friction losses are determined by L/D that is the ratio of the tube length to the diameter. A larger diameter tube will have less friction losses, if that is an issue. And also the roughness of the tube contributes to friction losses. Most plastic tubes have very low roughness, but it will increase over time with particles accumulating on the inner tube wall.


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