Many aquarists go to some considerable lengths to baffle sumps and pump flows to prevent small bubbles from being returned into the display tank. It has been suggested that such bubbles represent an irritation to fish, corals and other invertebrates and that they should be avoided. To be honest, I am unsure from where the origin of this perception came. However, it is untrue. Even the name is inaccurate the prefix micro would refer to bubbles too small to see.