sprewel1612

At what point are filters really not helping at all?
I have two tanks with a lot of filtration, a 90 gallon and a 30 gallon. I was also told at a fish store that at a certain point, extra filters aren't going to do any good to the tank (other than take up space/raise the electricity bill). At what point is extra filtration useless on a tank?

I've got cichlids so I think the current is ok. I calculated the size tank these filters can manage and the 90 gallon has 550 gallons worth of filtering while the 30 has 230 gallons worth of filtering. The specific devices are listed in my information. I wonder if taking a couple off would really make a difference...

soldieroffortune1974

There's really no such thing as too much filtration.The cleaner you can keep it,the less maintenance it requires.The filters don't use much electricity,and not expensive to operate.The filters are good for creating water movement,currents and gas exchange.Depending on the types of fish,some like more current,others prefer almost no current,other than that,I wouldn't say it's anything to worry about.

pepetj

I guess there must be an upper limit somewhere... but in general terms, the more filtration the better.

There are, of course, exceptions:

a fry tank is better served with a sponge only filter in order to remove the risk of being suctioned by the intake.

Some species are sensitive to water agitation and require calmed water, HOBs could be a problem more than a solution.

In small tanks, some filtration system make no sense in terms of cost (e.g. a Wet/Dry sump for a 20gal tank).

I keep multiple filters in most of my tanks. So far with good results.

Pepe
Santo Domingo

Steen16

I have 2450lph of filtration in a 250L tank Thats filtering the whole tank ten times an hour... can do nothing but good

Iron waffle

generally the more powerful the filter(s), the healthier the fish.

Tavel

I believe the employee was referring to the notion of "diminishing returns" whereby the usefulness of additional items falls as the numbers increase.

example, imagine you need a desklamp:
1 is good
2 is better, more light!
3, 4, 5? why? additional lamps don't yield much benefit after a while.

more lamps don't worsen the situation (they don't make it darker)...but they also don't benefit it.

You start to get that with aquarium filters too, but you have to take it pretty far IMO.

sirdarksol

An excellent question. As was said above, there's really no such thing as too much filtration, but that only sort of answers the question.

To fully answer the question; "When the filters reach the point that they are, more or less instantly, changing ammonia to nitrites and nitrites to nitrates."
Extra filters are excellent as they provide backup for in case a filter's motor runs out, to provide extra water polishing, etc... but the primary function of the filter is to turn waste into nitrates. Once you've accomplished that, anything beyond is simply backup and extra water movement (good for some fish, indifferent for some, and bad for a few)