Is your skimmer outlet as far as possible from the 3 baffle return? Micro bubbles at start up are common sometimes. I run course black sponges on my sumps before return chamber. They really don't get clogged like people think, plus it keeps the pump intake free of any small shelled organisms. I also think there is a biological aspect to the sponge. When I do clean it, 1/month during WC, it is full of pods!