Anyone know what might be happening to this poor favia and if there's anything I can do to revive? He was living on the sand bed for a couple of weeks... I don't know if he's being eaten? I raised him onto rock near the bottom of the tank for now.
Do you still have that starfish in you picture? I have seen them snack on corals if they are not getting enough food. You can cut the dead skeleton off if it is really bothering you. But it is not needed. First check for brown jelly on it and if it does have it shut your water flow off before you take it out to scrub it.
I would upp the feeding on the coral if you want it to recover quickly. They do like detritus so you can stir up your bottom to kick some into the water every few days. Or you can spot feed. Take some frozen brine shrimp and squirt some of the juice from when you are defrosting into the tank about 20 min before you feed. It will trick the coral into thinking food is in the water.This gives it a chance to get the tentacles out before all the food is eaten so you can spot feed it. This also works on getting other tricky to feed corals to eat.
Normally if it got stung it would have been way more damage and would not stop mid polyp like it did in the picture. That is something that happens when it gets eaten or damaged by say a rock falling on it. Was it near the gonipora when it was on the substrate? If it got stung normally a bacterial infection would have followed and it would have brown jellied up.
Don't get me wrong gonipora can sting. It is just not normally a clean line like that if it was stung. At this point it really doesn't matter anyway you moved it. Lol
While a good theory, the problem with that is magnesium would be a tank wide condition. You would see effects all over the tank and not just one coral with a few polyps missing.
i use the same method as kman a clear stop point between the live and dead is normally something munching as for magnesium i dose and keep it at a very high amount around 1460 on the salifert test so to impede feeding would have to be alot higher than that. I actually found my sps growth increased with higher mag and cal levels and higher mag and cal allows your coral to feed on even more amino acids which is a clear sign of increased feeding