Finger Leather Shrinking, All Other Corals Excelling

I've got a tank full of coral, and everyone seems to be rapidly growing and extending except for my one finger leather.
It was the first coral I bought I think, so it's been in the tank for about 4 months.

Up until about 2 weeks ago, it was about double in size.
a piece actually fell off, and I put it on a rock. The small piece that fell off isn't too much smaller than the "mother" piece now...

I give it DT's phytoplankton 2 times a week or so.

Anything else I can do to help it get back to where it was?
Like I said, everything in the tank is doing great and growing.

Here's some pics:



Here you can see a few white spots on the tips.
I assume that's not good.



And here's the little piece that fell off, that's doing better than the "mother"



Thanks