Ive been dealing with similar issues in my tank. Started with a small acan I bought from a lfs (and dipped prior to adding to my tank). It basically lost all its tissue in a matter of days. From there, all but one of my acans started dying off. Now my torches and hammers are slowly dying one head at a time. Not sure what the issue is as all my parameters have been stable. I suspect its some sort of bacterial infection thats making its way through my tank. Im ready to give up with LPS and just grow sps as they seem to be doing great.
I had the same issue months ago, ended up losing ever LPS in the tank. Nothing I tried stopped it from spreading through out the tank. I was so frustrated, I almost gave up on the hobby.
Sorry to hear you guys are going through / have been through a similar issue still with no "answer" as to what, why or how to stop it. Hopefully this thread may eventually lead to some answers.
My my remaining hammer coral still hasn't had any polyps bail, although a different one looks sick each day, some "recover" in 24hrs some look sick for a week. But so far none have bailed.
This week I collected (all quite plain) a fairly large acan, a medium heliofungia and a small moon coral, we will see how they are doing in a months time as that seems to be the rough time frame before coral is effected.
I also sought advice on an aussie fb page. It seems that the overwhelming majority of experienced reefers (who took the time to comment) are sure this is caused by heavy metal contamination and not a bacterial infection (they think it's likely from bad pumps leaking into the water even if they look and work fine). Apparently with bacterial infections polyps bail out much faster than one or two a day.
I'm not convinced my pumps are leaking heavy metals and don't know any other way metal could have gotten into my tank but to make sure I have ordered a triton test. I live "rural" so it will take a week to get to me and then a week to get back and then a few more days to get to triton but I will put the results up here when I get them.
After I get the triton water sample shipped off I will also be giving at least my Hammer coral a dip in betadine (anti bacterial) if not the other corals too. Even if it's just to make me feel better.
Instructions I've been given are 40 drops to 1gal of salt water, leave in for 10-15min, swirl every now and then, rinse in fresh salt water and back into the tank.