Sponge filter help!

I can't quite tell what is going on in the video...is the top of the tube underwater?

No its not, the tank isn't deep enough

Or the tube is too long. That may be your problem right there.

Perhaps you need to cut the tube so that the top is an inch or two under the water. Wiser heads may prevail.

I have a sponge filter that works just fine and the top of the tube is two-three inches underwater.

You could try the sponge filter in a deeper vessel filled with water where the top of the tube is underwater, to see if it works, then trim accordingly so it will fit your tank.

The top of the tube (the outlet) needs to be at least 1/2 way submerged. Air bubbles and a small stream of water will be pushed out of the tube. If it's too tall, you could probably just take the "7" shaped part of the tube off..the bubbles might bother your fish though. Does that make sense?

Here's a better video https://www.youtube.com/watch?v=rc96EGgws1M and I tried putting it in a deeper tank but it still didn't seem to work. I cut the tube shorter and that's the one thats in the video.

That looks more like I believe it is supposed to....now you may want to turn down the air flow so your betta doesn't have to swim against the current as much.

If there are bubbles coming out of the top, it's working. You can tell by holding the outlet just above the surface.

More flow means better filtration. If your fish can handle it, it's good exercise. If you need to turn down the flow, try poking a few pinholes in the airline near the pump.