Filter Is Stressing Out My Betta

My betta fish has an undergravel filter, and I think it's stressing her out. She had stress stripes and I couldnt find why. Then just today I turned the filter off to see if maybe that was why. And soon her stress stripes vanished! I think the filter was too strong. There were bubbles all only the top from the filter. But now what should I do? I have an oddly shaped tank so I can't have a hang on back filter. What are my options? Also, once I get a new filter what should I do while it is cycling? Should I leave the undergravel filter on?

 

Get a one of those air pump adapter that can make you adjust the air flow.

 

I didn't know there was such a thing!

 

Can I get one for an under gravel filter?

 

What should I do until I can get one? Leave the filter on or off?