Whats wrong with my Zoas?

[Lynchcon]

Hi guys,

Have these Zoas about 6 months and recently noticed they have become oddly shaped. See pic.

The centre is protruding above the outer rim.

Any ideas what's causing this? Is it a problem? If so, how can I fix it?

Thanks

 

[MERKEY]

Double check all your parameters including salinity.

This will give a good starting point.

 

[Lynchcon]

All parameters fairly normal and stable.
Sal/ SG 34/1.025
PH 8.2
Alk 9
The temp has been a little up and down as its winter here.

All the other corals are fine... and I thought Zoas were reasonably hardy, so dont think its parameters.