hammer coral
 

I have hammer coral that will not fully expand, all other coral are doing fine, (frogspawns, candycanes, brain coral, torch coral). I pick up this coral about 2 years ago with 2 to 3 heads on it and now has 18.
Change the carbon in the reactor, did a water change with no results. It's been like this for about 4 weeks now. As I mention all other coral are doing fine.

Salinity 1.026
Cal 420
Alk 2.7
Ph 8.0
No3 25

Any idea what could be wrong with it.

Is it being bothered by any fish? Or is it possible that it is receiving too much light/flow?

I don't think it's receiving too much light or flow, as it's been in that location since I got it, and the fish don't seems to bothered it.

It's started to look like this, 6-8 weeks after starting n/p biopellets. Which is the only thing that I added to my tank setup.

Just wondering could it have something to do with the pellets? My nitrate has dropped from 50 to 25 ppm.