I had very good coraline growth up until I changed out new bulbs and then all the coralline that were exposed to the lights bleached, but the areas in shaded regions continue to have that dark purple color. Did you change your lights recently?
Never trust a crustacean. It is because of that that I stopped keeping hermits in my tank... they just cause all sorts of trouble if they don't have enough food. A good mix of snails can yield the same power as a bunch of hermits in terms of cleaning capacity. The hermits will attack and kill...
