Oh i second Katty's idea. I've also used it on my Tetra Whisper 10i. It's known as a baffle. Good Luck! It really is quite simple and will make your Betta very happy!
Baffle Link
Hi Everybody!
My name is Aaron and i an just getting back into the world of fish keeping. About 4 months ago, my Betta fish died and i didn't have the time to get back into the hobby. Now, with the end of the school year coming, more and more free time is coming.
Now i have a five gallon tank...