What Exactly Makes A Tank "Over Filtered"

[Nemesis]

When talking about over filtered tanks, the most common thing we hear is gph(gallons per hour). But is the gph of a filter everything? What about media? Can a filter with a high media capacity and a lower flow rate be equal or better than a filter with low media capacity, but a higher flow rate? Example: If you have two 55 gallon tanks, one with an AC110, and the other with an Eheim 2217. Would the one with the AC110 be considered more over filtered? Or if you take two of the same filter, and fill one with high quality media, and one with low quality media, wouldn't the one with better media be much more sufficient, and therefore more overfiltered?

So my question is, what do you feel makes a tank over filtered? Flow rate, or media? A good example is say... an FX5 and an Eheim 2260. Both are rated for up to 400 gallons, but the FX5 has a flow rate of 925gph vs the 2260's 500gph. But the 2260 has alot more media capacity. Would the FX5 provide better filtration just because it has a higher flow rate?

 

[Bderick67]

I think calling it unnecessary filtration would be more accurate. None of the examples you gave are overfiltered.

As far as the two larger filters go, I would think the higher flow rate would benefit the mechanical filtration, but even that still has to do with the design of the filter.

 

[12 Volt Man]

I think there needs to be a cost factor involved too.

eg. people want to put twin FX5's on their 90 gallon tanks, which is almost $800 filtration (in my area (canada) if you include taxes) when in reality, an XP3 for 1/4 the cost would work just as well..

I think overfiltering comes when we spend insane amounts of excess money and we don't really accomplish any real benefit that much cheaper filtration would not already accomplish.

 

[dragonfish18]

sum ppls opinion a tank can never be over filtered but it really depends of your stock and how much output they have.
and i guess with faster flow rates it really depends on the structure of how the filters built they might work biologically but still lets an amount of debris back in the tank. as well as were u place the intake of the filter and the current...wen it comes down to it i think its preference weather a tank is over filtered

 

[Bderick67]

And sometimes the overfiltration is a result of other reasons. I have a couple tanks that I run twin XP3s on where a single XP3 would do fine. But I do this for the security of redundant filtration

 

[jtalley]

An engineers take:

If you consider a volumetric flow, Q [m^3/s], and a flow area through the media, A [m^2], the filter with the lowest superficial flow velocity, Q/A [m/s] will yield the highest interaction time between the media and the fluid for the bacteria to do their job. Since the rate at which the compounds are converted should be independent of local concentration, there is no difference if the compounds are removed by a slow flow or high flow (higher local concentrations will exist at the onset of filtering with slower flow than higher flow if in both cases the media convert at the same rate). For a slower flow rate, and constant source from waste, the concentration will be higher in the slow fluid because it is being spread out over less fluid. However, a higher Q will yield better mechanical filtering yielding a "cleaner looking tank". Moreover, since the time scale of liquid movement due to filtering rate should be far higher than the concentration diffusion rate (dependent on the square of concentration which is already small before squaring) that the location of the sources should not matter, but again yields a cleaner tank and keeps the media from clogging. Keeping the media from clogging is more important, since fouling will decrease the effective surface area, raising the superficial velocity, thus reducing the interaction time of the fluid with the media and require more "passes" of the fluid through the media to remove the same amount of compounds than a non-fouled media. Just a technical rant...

 

[Nemesis]

An engineers take:

If you consider a volumetric flow, Q [m^3/s], and a flow area through the media, A [m^2], the filter with the lowest superficial flow velocity, Q/A [m/s] will yield the highest interaction time between the media and the fluid for the bacteria to do their job. Since the rate at which the compounds are converted should be independent of local concentration, there is no difference if the compounds are removed by a slow flow or high flow (higher local concentrations will exist at the onset of filtering with slower flow than higher flow if in both cases the media convert at the same rate). For a slower flow rate, and constant source from waste, the concentration will be higher in the slow fluid because it is being spread out over less fluid. However, a higher Q will yield better mechanical filtering yielding a "cleaner looking tank". Moreover, since the time scale of liquid movement due to filtering rate should be far higher than the concentration diffusion rate (dependent on the square of concentration which is already small before squaring) that the location of the sources should not matter, but again yields a cleaner tank and keeps the media from clogging. Keeping the media from clogging is more important, since fouling will decrease the effective surface area, raising the superficial velocity, thus reducing the interaction time of the fluid with the media and require more "passes" of the fluid through the media to remove the same amount of compounds than a non-fouled media. Just a technical rant...

Let me go over this one more time...lol.

 

[ron521]

As I use the term, overfiltering means using either a much larger filter, or more filters than are needed, or both, to achieve your desired water quality.
For example, on my 75 gallon community tank, I have TWO Lustar HydroSponge IV. Either one of these is supposed to be good for tanks "up to 80 gallons", and I have two of them, so potentially, I've got 160 gallons worth of filtration on a 75 gallon tank.
That's overfiltering.
By the way, they are the ONLY filters on that tank, it's heavily planted with Anubias, and home to several dozen tetras, cories, and a few other species. Water quality is EXCELLENT.

 

[Nemesis]

That's kind of what got my question going. You can have a 2260 that's rated for 400 gallons, and a fx5 that's rated for the same, but the fx5 has alsmost double the gph. How do these companies come up with their maximum tank sizes the filter can handle? And if you had two 75 gallons, one with a fx5, and one with a 2260, which would be considered "more overfiltered".

 

[tcarswell]

That's kind of what got my question going. You can have a 2260 that's rated for 400 gallons, and a fx5 that's rated for the same, but the fx5 has alsmost double the gph. How do these companies come up with their maximum tank sizes the filter can handle? And if you had two 75 gallons, one with a fx5, and one with a 2260, which would be considered "more overfiltered".

Well Eheim I believe rates their filters higher because they typically hold more bio media than their competitors at Hagen and hence can take a larger bio load. However this is their logic I don't necessarily agree with it. I would not filter a 400 gallon with a 2260 alone. It will achieve 0 ammonia and 0 nitrite on a decent stocked 400 gallon, but as far as mechanical debris and water circulation in the real world you would have to add power heads or other filter IMO.