Acro tissue dying

[Acrofiend]

Alk: 9.0
Calcium: 410
Nitrate: 10
Phosphate: ?

I do weekly water changes. I don’t run any chemical filtration. Just filter floss.
All other acros are doing good.

 

[ndrwater]

Where are you talking about specifically on this piece? With Acros, if Alk or lighting isn't an issue, it's usually flow..
As some branching corals grow, the flow to the middle is lessened and can cause tissue death from the inside out.