I wonder if the problem is due to the fact that both systems are so different... Different salts, calcium additive methods, etc. Big change from one to another?... Just a thought with it being a new tank.

No way...not when the small tank has been established, happy and stable for years. Three coral have now all died in the small tank that had been growing perfectly well there for years. All within 48 hours of my trying to "rescue" that small piece.