Hi...Will the betta be the only fish in this tank? I have 2 bettas in a 5 1/2 gallon divided tank. Before I set this tank up, I had one betta in an Eclipse 3 gallon tank with a bio-wheel filter. I liked this filter; it was nice and quiet, but it created way too much current for the betta and he hated it. Someone told me to cut off some of the impeller fins -- every other one, and that would reduce the outflow. I didn't try this though. I just got the betta another tank, the 5 1/2 gallon one (and another betta to go in there too)! Maybe clipping the impeller fins would work for you.
As others have said, you're probably over-filtering. I know my bettas hate any kind of current, so if your goal is a betta in this tank, you should filter it so that there is no current. Save the filter to use on another tank, or move it into your minnow tank. In my betta tank, I use a sponge filter. It's a Jungle Jr. dirt magnet, for 5 gallons. Jungle has different sized dirt magnets (sponge filters). I use a small air pump, a Tetratec 12, and it makes bubbles, not waves. It's aerating the water a little; obviously not as much as a larger filter, but it's ok for the bettas. I have a 3 valve gang valve too, that is between the air pump and the sponge filter. I adjusted the gang valve until the bubble rate was good. I have a pretty steady and somewhat fast flow of bubbles, but it doesn't make any current. I opened one of the other gang valves a little to just let some air from the pump out into the room, but it's such a little amount, I don't hear any hissing noise. The reason I got the gang valve was so I could adjust the airflow from the pump without damaging the pump -- the extra air has a place to go and it won't put extra stress on the pump, and the bettas are happy.