Originally Posted by mikestanked
Would the zoa not spreading have anything to do with excessive water flow?
You never want direct pounding from a powerhead or return pipe on them. Many zoas live in areas of the reef with powerful surges and sometimes the even get exposed to the air when tides are out. They can take strong flow, but constant blasting is a bad thing (more because of the toxins they coat themselves with in order to protect themselves than because it might do harm to them). If they constantly have to produce their toxic slime coat it'll leave little resources for them to use to multiply and some believe it isn't good for other sensitive corals in the same tank.
Basically, even though they can deal with hard flow in nature most people avoid hard direct flow in their tanks.