Emm... Phosphate is not that crucial as long as there isn't an algae bloom in your tank... Magnesium is good to know as it affects KH and Calcium.
NO3 you can try chemical (bottled solution, sulphur-based reactor) or biological (denitrator such as NR400 or 1000)
As for coralline, mine all over... basically they need very high calcium level... 500 is good. They also need Strontium to grow. I heard from somewhere... they also prefer lots of actinic blue