What size tank?
IMO,some coralline reguires low to medium light.The reason I say that,I got coralline growing almost too good except for in the top 4 inches under the water and Im running 432 watts of light.
I think temp. play a part in it( at least in my tank).Mine grows better in temps between 74 and 79 degrees.
You state that your dosing for calcium,mag,stront. and iodine.Are you testing for those?It could also be that the stront and iodine levels are to high.