Overfiltering

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mobiusnu

Aquarium Advice Activist
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Jan 21, 2005
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I've heard it said many times here that one can't overfilter their tank. However, at least from a biological filtration perspective, it seems that as long as the tank has 0 ammonia and 0 nitrite, there is no biological filtration beyond that for the filter to do. The only thing to be done from there is mechanical and possibly chemical filtration, but those don't seem to be big issues in a cycled tank.

For instance, what additional benefits are there to turning the water over 10 times/hour instead of 5 times/hour if at 5 times/hour the water quality is good?
 
Ha ha, you've stumbled onto one of the Great Urban Legends around here. As in, one of those things users often say, only because they've seen it said by others before.

I think what they mean is that overfiltering your tank will not cause any harm. Underfiltering, obviously, will. I think the term you are defining is excessive filtering. It doesn't hurt, but is certainly a waste.

Another of my favorite Urban Legends people like to sound authoritative on is "goldfish are messy." That may be true, but I make people feel uncomfortable by then asking them what difference that makes in a properly cycled tank. Gets pretty silent at that point. :twisted:
 
Well, I still think it helps. In a few of my tanks I overfilter with multiple filters- a big help if one of them ever quits on me. Plus, if you are using HOBs (which is all I can afford) how could it not be helpful to have a filter circulating water and sucking up detritus on each side of the tank? Even on the tanks I overfilter with only one filter- better safe than sorry IMO.
 
multiple HOBs

I like running multiple HOB filters as well, for the same reasons. I rotate replacing media and filters and such and IMO, this helps keep things stable as far as bacterial populations are concerned.
 
I only have one HOB filter, but was thinking of getting another for the reasons posted above, becasue it really is only pulling water in on one side, and what if it quits? it would be nice to have a back up. However, my water parameters are all perfect as far as ammonia and nitrites being at zero with just the one HOB.
 
Relative newbie speaking (~6 months in the hobby)

What of the argument that since bacteria can live on most any surface, the area available on decorations, tank walls, etc, makes biological media unnecessary? Taking idea further, why not remove all powered filtration altogether, since you probably depend on pwc to lower TDS/DOC? Also, mechanical filtration can certainly be an issue in cycled tanks with messy fish for the detritus mentioned by Severum Mama. Also consider that turnover rate is simply a guideline to help in purchasing decisions, as "/gal is a guideline, and filtration rules *may* have something to do with encouraging oxygenation with surface turbulation. I don't think these are Urban Legends as much as rules of thumbs: nothing applies to every situation. Good to think outside thumbs, of course. :)

Re: Goldfish: I think the messy argument is used as justification for the 10-15gal/goldfish rule of thumb, which makes sense because high ammonia produced will be diluted with higher volume (> rule than "/gal), limiting NO3 in terms of ppm if pwc percentage stays constant. Don't know for sure, though.
 
If you can manage sufficient biological filtration without a filter, then by definition of "sufficient" you don't need a filter for biological filtration. I doubt you could actually achieve that, but if you can, great.

The only real justification for overfiltering I've seen on this thread is people are afraid that their filters will die.
 
Just a thought,,,, lets say you had 1 inch per gallon and your filter was bare minimum, just enough medium and flow to keep the up with your stocking level. Wouldnt another filter or a more powerfull one enable you to break that "rule" or at least bend it? I will get a lot of flak for this, Im sure, but I feel that if water parameters are stable and the filters can keep up with the added load, then overstocking is gonna work in some cases.
 
hardcyder said:
Just a thought,,,, lets say you had 1 inch per gallon and your filter was bare minimum, just enough medium and flow to keep the up with your stocking level. Wouldnt another filter or a more powerfull one enable you to break that "rule" or at least bend it? I will get a lot of flak for this, Im sure, but I feel that if water parameters are stable and the filters can keep up with the added load, then overstocking is gonna work in some cases.

this was discussed in a previous thread....

Overstocking comes in many forms, NOT just water quality.

you can be safe in terms of water quality, but that does NOT mean you are safe in terms of "swimming space/territory"
Fish need open areas to swim.
Even schooling fish need space amongst themselves.
Fish do not like to be constantly bumping into another fish.


Back to the topic.
In my opinion, its impossible to overfilter.
however, too much filtration becomes reduntant, a waste of money (why buy a canister for a 10 gallon) and a waste of electricity.

also, too much filtration can be stressful for the fish.
Especially if the more powerful filter creates stronger currents.
Fish like to have peaceful/calm places in the tank too.
 
IMO "excessive" filtration is a personal choice some people make based on their personality. If you tend to overdo things, excessive filtration sounds like a good idea. If you are more cost conscious and like to use what is "enough", then you don't use "excessive" filtration. I agree that with some fish, too much current is stressful. Some fish thrive with some current as it is part of their natural surroundings. The amount of filtration should be accomodating to the fish in the tank and, as you said, is not a license to overstock.
 
I use canisters & hob's on 2 tanks. I like the idea of having an established filter if the other one quits and being able to change the filter media alternately.

Dave
 
I think that redundant filtration is for people that dont have tons of extra filters just laying around like me.. JK

I think that 5gallons per hour is adiquit for most filtration needs..
and a planted tank with 2wpg and heavy planting with medium to low bio-load can get away with little to no other filtration..(other then the plants)
it really depends on the setup and needs serious consideration in the planning stages of setting up a new tank IME and IMO.. HTH
 
hardcyder said:
Just a thought,,,, lets say you had 1 inch per gallon and your filter was bare minimum, just enough medium and flow to keep the up with your stocking level. Wouldnt another filter or a more powerfull one enable you to break that "rule" or at least bend it? I will get a lot of flak for this, Im sure, but I feel that if water parameters are stable and the filters can keep up with the added load, then overstocking is gonna work in some cases.

As others mentioned, there are other considerations aside from the bioload. Yes, you could add more filtration and handle more fish waste. But you'd still could have problems with territory, swimming space, and things like that.
 
dax29 said:
IMO "excessive" filtration is a personal choice some people make based on their personality. If you tend to overdo things, excessive filtration sounds like a good idea. If you are more cost conscious and like to use what is "enough", then you don't use "excessive" filtration.

I'd just like people to be more clear about what exactly they're recommending. If people recommend having two filters for redundancy purposes (and that causes overfiltration), that's fine. But they need to make that suggestion on the basis of redundany, not on the basis of filtration effectiveness.

But occasionally people will say that others "should" get a bigger single filter for a particular tank. That doesn't further the redundancy goal at all. Generally, all that does is move more water around.
 
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