Okay.
Micro-bubbles are not likely to kill your corals. They are unsightly, but if you go diving around a reef there are tons of bubbles. Small chance that any harm will from from micro bubbles. Bubbles are not deadly.
It can take up to 3 weeks for a skimmer to break in and stop forming micro bubbles. It may take 3 days. What needs to happen is for a skimmer to develop a surface of bio-film. It happens with all skimmers. When you first turn it on, it creates copious amounts of bubbles, leaking out micro-bubbles. Then the coat of bio-film starts to cover it, and the bubble production drops, and eventually the micro bubbles become manageable or none escape the skimmer. Some designs always create micro bubbles. If this happens in a sump model, easy enough to trap and keep out of the tank.
but all skimmers have a break in period of up to 3 weeks, though it is very unusual for the break in to go past two weeks and often under a week.
