Sun coral necrosis?

[sassyonmane]

Unsure which section to post this in but I’ve had this sun coral for over a year, started off super small and I grew it out and was super healthy, extending every night until sunrise even without food but when I moved it to my other tank it was fine for 2 days then stopped opening and eventually had its tissue getting blown off when I turkey basted it leaving yellow dots all over it, what would cause this? And should I leave it or frag it or iodine dip or cipro dip it, should I move it back into the old tank?
In the old tank it was getting little to zero flow and in the new tank it was getting pretty high flow in the sump