GSP and xenias are fine - but don't place them into a tank unless you anchor them to a rock and isolate (they will spread and overtake everything). Here is exhibit A, B, C (etc.) I let a small (we're talking 1") GSP colony thrive on the side of a rock, thinking "how harmless could it get". 6 months on and it's overtaken what was (once) a rather nice zoanthid colony, duncan colony and favia. Oh they're still they're - just overgrown by GSP.
More proof of "Do as I say" and "Not as I've done"...
More proof of "Do as I say" and "Not as I've done"...