Wow, that's a great deal.
The pump actually creates a lot of current for that tank, so you'll probably want to turn it all the way down. That still might be too much for a betta.
I've read of people making spraybars, restricting the flow with some sponge or floss. One person put a hole into the tube both to create more flow in the 2nd chamber (good if that's where you want to hide the heater) and reduce flow into the tank.
I thought maybe a bunch of tall plants might break up the flow, but since the return looks like it's on the front of the tank, that would also block your view.
Oh, and there's room under the sponge between the two chambers to stash purigen or something else if you want. Maybe one of the small, no-settings "betta heaters" would fit down there.
Last edited by jrh; 11-27-2013 at 02:42 AM.
Reason: Added spraybar suggestion