Acro tips peeling

[Glassfish]

I've had this frag for about 6 months or more. Came from a friends low nutrient tank so it got dark in mine and growth was slow. This last month is has taken off growing and the colour getting much better, living up to its name of Hot Pink but now I've noticed over the last few days that one of the tips that hasn't grown much is starting to peel. Polyps are extended and other corals are doing fine. Any idea what's up ?

Parameters have been stable too
Alk 8
Ca 400
Mag 1300
Ph 7.9

Tip in question is right in the centre of the pic, the growth on the upper tip is from this last month so it was doing well

 

[Glassfish]

I was running bright well Xport for phos removal until this morning as I wanted to get more nutrients in the tank.

I have been feeding unstrained Brine shrimp to my fish every day as well as feeding reef roids.

Just adding that as my thought was too low of nutrients but I'm not sure