One important, but often overlooked factor is stray voltages in your tank. They can be caused by any bad electrical equipment in your tank. You can test it by using a meter to measure voltage from the tank to ground. If you see any, unplug each of the items in your tank until you find the offender. Then replace it.
Favia corals live in all kinds of light and water flow conditions, so you may need to move it around a bit. Consider trying a place where the light isn't as bright.
It may also help to feed the coral. You want extremely fine food for this. Some people siphon out a bucket of tank water, put the coral in there, and then feed it in the bucket for a few hours. Then return the coral to the display tank, and top up the tank. This lets the coral feed undisturbed, and you can feed heavy, since the water doesn't go back in the tank.
Check your water parameters, especially calcium, alkalinity, and pH. Even if they are ok, if may be worth a large partial water change. If the coral perks up, you may need to do more water changes.
