You might try Vic C additions. I have had good luck with it. There is a thread on this forum about it. RPE sometimes can be problematic. Make sure they are in low/med light and good flow. Could take a month before they reopen.
I have tried after reading a thread on another site, though I don't recall which, maybe RS, about injecting iodine into the polyps. I have tried this and it has worked on PEs. I will not go into it as I have only tried it on a few that were not opening and though they are now doing fine, I do not know any details except that I used a diabetic needle and injected about a drop into each polyp and it helped them. Other than that I cannot give any info. I used Kent's Super iodine BTW I recall the thread calling for. I did some RPE, PPE and HPE and they all are now open and doing fine. I did some zoanthus but they eventually faded away.
I would try Vit C first, moving them to the right location and reserve this if all else fails.
Oh, also did some Lord of the Rings and some Devils Armour which responded well and are now open.
I tried to find the link and had no luck so cannot give any info on this, sorry. Maybe someone else knows about it.