Becasue the clean water coming out of the filter is hitting the surface water of the tank, it's like jumping into a pool and you get all of those bubbles around you, same thing, except the water coming from the filter is doing the jumping.
That is, how low is the water level in the tank? Is it low enough so that the water coming from the filter goes through air then hits the water?
And what kind of fish do you have in that tank? What size is the tank? You don't need to be doing water changes everyday, if it's just a community setup, maybe one every 2 weeks.