Looks happy there but also looks like a lot of the skeleton poking through around the top. As noted by others low NO3 and PO4 could be an issue if it's not getting enough nutrition. Ca and Alk and Mg are also very important for stony corals. Especially stability for those 3. You could try target feeding a little to help with the nutrition if you haven't.
I would also be looking at some better test kits. The Api kit is notoriously not so good...
I use the Hanna DKH checker for Alk, ultra low phosphate for PO4. Salifert for Ca, Mg. Nyos is good for nitrate although I have recently switched to the Hanna high range NO3.
I would also be looking at some better test kits. The Api kit is notoriously not so good...
I use the Hanna DKH checker for Alk, ultra low phosphate for PO4. Salifert for Ca, Mg. Nyos is good for nitrate although I have recently switched to the Hanna high range NO3.