Sponge filters

dalto

dalto

AC Members
Jun 12, 2006
69
2
8
So, I have a sponge filter on my 10g qt tank. I hooked it up and it is running but I don't really understand how it works. An air hose runs down through a plastic tube into an outlet. It blows air into the outlet, which in turn goes back up through the tube in the form of bubbles. How does this provide filtration? Can anyone provide some insight?

For reference, this is the filter that I have:
https://www.petsolutions.com/Hydro+Sponge+I-I-32500910-I-C-23-C-.aspx
 
What happens is the air bubbles draw water up the tube. The water that is drawn up the tube pulls water into the sponge and the sponge grows beneficial bacteria in it. It is the bacteria in the sponge that does the filtering.

That is a down and dirty but it is the basic idea
 
Interesting. How come the water just doesn't come down the tube where the bubbles are rising?

Also, how much air pressure should I have? Mine is bubbling like crazy.

Thanks again.
 
Because the bubbles are going up, moving the water around it up as well. So, if hte water is going up, it needs more water to keep going up, hence the vacuum effect pulling water through the sponge... Same thing with UGFs, but using the slotted plate instead of a sponge. I belive you can have it going pretty strong, unless its making more surface agitaiton than you want?
 
You can also power a sponge filter by dropping a powerhead onto the top of the tube, which increases the draw into the sponge significantly.
 
I'll look for an illustration, but the flow through the sponge and up the main tube is created by water trying to reach an equilibrium pressure.

Have you ever stuck a clear drinking straw in to a glass of water and blown bubbles? If you do it slowly, as you increase the pressure in the straw by blowing air in, you will see the level of water in the straw go down and actually be lower than the level of water outside the straw.

When you take your mouth off the straw and release the pressure, the straw water level comes right back up due to water rushing back in at the bottom.

On the sponge filter you describe, the air entering via the small tube displaces some of the water in the main tube. This creates a column of water that in effect weighs less than a similar column of water outside the tube.

Since water wants to reach equilibrium, the "heavier" water outside the tube pushes through the sponge and up out of the main tube, creating flow. If you lower your water level down to the top of the tube, you can see this effect by observing a small "fountain" of water shooting up.
 
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