#1,Yes you can have live rock with a UV...The UV willnot hurt it at all....#2,Although a skimmer will remove some addatives,calcium is not one of them....and #3,Other than using caution whan medicating a tankwith live rock,I can not think of a single othe problem...Most people(including me) Highly reccomend using live rock with any saltwater tank...The benafits are too numerous to count...