It's just the way the water comes out of the Bak-Pak. Same way my CPR refugium is. The microbubbles, they will go away in a few days after the skimmer breaks in. Give it some time.
After it breaks in, there will be hardly any microbubbles. But, the way that thing is designed, you are going to have some large bubbles--about 1/4" size. They don't splash a helluva lot. No way to stop it. It's just the design.