I use a EuroReef ES135, which is basically the same as the "old" RS. On mine the outlet pipe is a strait pipe sticking strait up vertically. I have no bubbles because the outlet pipe has a foam sleeve that covers it. The returning water comes out the top of the pipe and down through the foam sleeve.
Does the RS have the outlet pipe that goes up like mine with the elbow comming off of it and pointing back down?
I am not used to that configuration, so my way may or may not help.
Is the skimmer new? I have heard from others that the RS may make bubbles until it breaks in. Just a thought.