Sponge Filter Flow Too Strong

So I accidentally purchased a sponge filter that's a little big for my tank (it's a 20 gallon high and the filter is good for 'up to 60g'). I added a betta in and, while he's swimming pretty good, he's getting knocked around a little bit when he gets just past the halfway point of the tank, as well as at the top (the bubbles are making the entire top of the tank wave up and down). He seems fine if he stays toward the bottom on the filter side of the tank, but if he swims into the upper part, he has to work just a little bit harder to swim.

I've got some plants coming in the mail, but I'm afraid it won't be enough to slow the outflow of the filter (especially because there's only two taller ones coming in. I've never done plants, so I'm just testing them out and whatnot). My air pump only has one level, so I can't turn it down.

My question is, is there a good way to soften the current in the water?
I thought about buying an extra sponge and cutting it fit around the little clear tube at the top of the sponge and a little above, but I don't know if that's actually going to do anything because the bubbles are still going to be coming out and reach the top of the tank. Would it be beneficial to put a small rock or two on top of the out going tube (if I can get it to balance safely) so it spaces the bubbles out?

 

if I were you, I would cut the sponge to fit the filter

 

If you can't turn the air down at the pump you could add a tee piece and two flow control valves, one in the line to the filter and one just to the open air. By adjusting the two valves you can adjust how much air goes to the filter and how much is leaked out.

 

And what filter did you purchase??

 

I saw a video that put an air stone inside the filter tube and it made more bubbles but less turbulence.

 

The sponge itself doesn't really affect anything- it's the air pump. As mentioned you can create a bleed valve to decrease the amount of air going to the sponge as well as put an airstone inside of it.

 

Heron
I'm lucky I'm a bit of a packrat when it comes to 'accessories' because there was a valved t-split in the package with the air pump! I stuck that on and now it's all good! The bubbles are much more manageable and still doing their job! I think that's the quickest I've ever had an issue solved; thank you so much!

Cichlidude
I got an aquaneat aquarium bio sponge. I've only ever used HOB before and wanted to try a sponge filter out and just bought the wrong size -_-''''

 

It's hard to say a sponge filter is too large for a tank in my opinion, unless you mean aesthetically.

Now I can see someone having an undersized sponge filter that won't cycle a tank.

When a filter is rated for xx gallons, that is just marketing go they can have a hierarchy of filters to sell to people with different sized tanks.

That's why I have both a sponge filter and a HOB "rated for up to 20g" in a 10 gallon tank.

Good to hear your air pump issue solved!