Hi Thashan, I have the 200lt and the same skimmer, what cause the problem is that the blue sponge at the bottom of the skimmer has come loose.
I have put a small piece of live rock in there to keep it from moving with the juwel Carbon sponge.
Couple of other questions..... How new is the tank and Skimmer? Is the air valve completely open?
I found that after awhile my skimmer did settle down and no more bubble came out. only if I clean it out completely and change the Carbon does it start the bubble for an hour or so again.