View Full Version : How does a Sponge filter work?

05-09-2003, 04:18 PM
Does it use an undergravel filter and just pull it up that way?

I've seen the sponge filters in tanks but I never knew how they work...

Can anyone explain it?

05-09-2003, 09:39 PM
i moved your thread to this forum so that it would get a better response.

05-09-2003, 11:00 PM
Mostly biological filtration mainly. The sponge has tremendous surface area to grow and collect nitrifying bacteria that will break down waste and keep your water quality better. There is some mechanical filtration in that the air pushed through the bottom tube will create a bit of suction throught the bottom of the sponge whick will collect the waste.

The air will also create surface ripples in the tank to oxygenate it.

05-10-2003, 05:03 AM
So does it connect to an undergravel filter and air pump?

And thanks Gypsy:D

05-10-2003, 08:58 AM
It does not connect to an undergravel filter, as all it is is a sponge with a tube cominng out of the center. It runs off of an air pump though.

05-10-2003, 09:46 AM
A sponge filter can either be driven by air (as described above) or fitted with a small powerhead.

Basically, air is driven into the interior of the sponge. That air rises, and in doing so creates a gentle suction action from the outside of the sponge into the interior as water is required to replace that which is lifted out by the rising air.

With a powerhead, a small motor is fitted to the top of the sponge pushing water up or out from the interior of the sponge. The same physics are at work as with the air pump drive.

The filtration theory is as described in the post above. The sponge serves as a host to a large amount of bacteria. That bacteria converts the dissolved wastes in the aquarium to relatively harmless nitrate. That nitrate can be removed during regular partial water changes.

The bacteria involved require oxygen to do their work, so the constant flow of oxygenated water through the sponge provides that.

Due to the gentle sucking action of water through the sponge, some degree of mechanical filtration takes place. But mechanical filtration pleases just an aquarist's eye, it is biological filtration (the bacteria noted above) that converts harmful dissolved waste into relatively harmless nitrate. You can have weak mechanical filtration and strong bio-filtration but not the other way around if you want to keep fish in good health.

As far as air vs. powerheads are concerned, air may actually do better. The bacteriological processes taking place require some time, so a powerhead may actually move the water too quickly through the sponge. There are very small powerheads available, though, that are apporiate for use with sponges.

If you're wondering why people would use powerheads instead of air (keep in mind a good air pump can power multiple sponges while a powerhead powers just one at a time)..... I have found that the rising bubbles create more noise than I'd like (if the tank is in a room other than a fish room). Also, the powerheads can be aimed so that their currents stir up the bottom layers of the tank better so that a hang on back (HOB) power filter can serve a mechanical filtration purpose better.

You see sponges in use in most of the tanks of breeders and serious hobbyists. Scores of sponges can be driven by one large air pump, so they are an economical way of providing filtration. Also, they do that job very well (even if in a rather industrial looking manner). They are also good for breeding tanks since they do not such fry and young fish up into the filters. Also, the serva as a feeding site for fry since the surface of the sponge can host small bits of food and nutritious organisms.

05-12-2003, 11:48 PM
So a powerhead would be good if I wanted to stir up a 120 gal tank a little more....

I'll have to look into that....

Thanks guys:D

05-13-2003, 11:35 AM
You could just get one of those Aquaclear powerheads that have the "Quick Filter" attachment. They basically function solely as a mechanical filter and water movement device, but if you got a sponge with a powerhead big enough to move a lot of water it would be too big to get any significant bio-filtration benefit (i.e. the flow through the filter would be faster than ideal).

What is you primary filter on your tank?