I have kept the torch coral since setting up the tank and the leather coral since its early days, so I have grown especially attached to them. Compared with my other, relatively still corals, their gently waving polyps are what make them so appealing.
It was hard to watch when their polyps pulled all the way in and they shrank. I kept coming up with theories and trying things, and it really wore me out. In the end, though, it seems the biggest problem was the temperature.
After buying an OKE-6428HC cooling/heater temperature controller and setting it to 25°C, the torch coral is definitely looking better.
The mouth is still visible in the middle, but the outer polyps are growing well and it looks fuller. The clownfish looks happy too.
It was probably a buildup of several factors: a single head splitting into two, high temperature, insufficient nutrients, and so on. But in my tank, temperature felt like the biggest factor.
I tried all sorts of things—phosphate dosing, adding activated carbon, and more—but it turned out the glass thermometer was the issue…
If your corals have been looking worse and you have only been using a glass thermometer, it might be worth checking its calibration.