Sponge Filter Q.: How Do I Know It's Working?

[soritan]

So, I've had a commercial sponge in my tank for quite some time, but I was never really sure if it was working properly or not.

I tried to photograph the filter a few times, but gave up and made this jpeg after many attempts to get my old camera to cooperate.

As you can see (Hopefully), the air is escaping out of the tube, instead of out the sponge. As I've never seen a sponge filter before this one, I'm not sure if that's normal or not.

Air comes in the air line, goes down to the stone, and comes out the tube. I tried to illustrate that...

 

[Tolak]

That's how they are supposed to operate. The air pulls water up with it, the water in the tube is replaced through the sponge. You can see how much water is flowing by lifting the filter towards the surface of the water, leaving the top of the tube level with the surface.

 

[soritan]

Aah, I see. I was wondering about that.

I wonder, does the sponge suffer massive bood bacteria die out when the air pump is turned off for a long period of time? I recently had to replace my air pump, and so the thing was off for a good month during that time. I'm not really concerned about it, that tank has 2 HOB filters on it already, I'm just curious.