I hope the frag does well for you.
Questions for you about the barnacles and white stuff, though - has the white stuff been growing on any healthy parts of the coral/have the healthy parts been receding away from the white stuff?
Was there any white stuff around the barnacle when the hammer started receding?
How do you know the barnacle is what irritated the hammer (I don’t doubt you that it did, I’m just wondering what indication there was - for example, did the flesh recede around the barnacle itself without the presence of the white stuff nearby)?
From everything I’ve heard, regular barnacles fair poorly in our aquariums, but I’ve been hearing recently that these coral-boring barnacles tend to do better/live longer in them (somewhat unfortunately).
That said, this is the first I’ve heard of barnacles actually damaging a coral (i.e. causing irritation and receding flesh) - they usually just cause deformities as a result of their burrows in the skeleton from what I’ve seen. Since this is the first time I’ve heard of something like this happening, I’m wondering if the irritation was caused by barnacle itself (which would lead to me wonder if hammer corals are particularly susceptible to irritation by the barnacles methods of feeding or by the process of the production of their shells), or if it’s the white stuff growing on your coral (which I would guess is a sponge - some sponges are known to produce chemicals which are used to combat corals and such for space to grow in the wild, so if the cause might be the white stuff, I’d guess it’s a potentially invasive sponge with anti-coral chemical defenses).
