I don't have an answer for you
I'm just a newbie myself but
After reading alot of posts
These experts here are going to need more information
Like tank size filtration
You parameters lighting type/ how long you run them
Additives
Anything you ever thing you got for your system
This could be a bad sign, or nothing to be concerned about... For example, all of my birdnests have white tips. All of my birdsnests are growing, hence the white tips. It takes a bit of time as the coral skeleton grows for the symbiotic algae to grow and provide the colouring we all enjoy.
I agree, a pic would help. My BNs have always had white tips too, but that is growth tips and not tip burn. Is algae growing on the white parts, or are they turning brown after about a week?