The lack of corallines is relatd to the level of phosphate. I bet if he takes a phosphate reading it will be high. Corallines recede quickly and turn white then, micro algae in either brown or green appears and smothers everything. Source water is almost always the problem, sometimes too much flake food without water changes and phosphate resins being used.
Please test the water for nitrates, phosphates, calcium, and Alkalinity. Poor lighting will create very dark purple corallines and intense lighting will create very bright pink corallines. Therefore, I suspect it is a phosphate issue.