I was wondering about microbubbles recently too, as I'm getting them from my canister filter. I did a search here on Canreef, but couldn't find an answer, one way or the other. I did another search elsewhere (Google? I forget.). Anyway, I found this: (Myth #14).
http://www.reefkeeping.com/issues/2004-01/eb/index.php
Cheers,