It is fairly normal on a new set up, the pumps are stronger than they will be after a month or two of use and the plastic repels water and some air is expelled with it. After it has broken in this will reduce sharply. If the tank is new and the saltwater is fairly fresh or some additives like a stress coat or slime algae killer or certain vitamins it can be made worse. For the time being you can close the front shutter over the intake, this forces the skimmer to recirculate and will reduce bubbles but over 2-3 weeks it should put out far less bubbles.