Sorry to hear Mark.
Not sure if I understood what you meant about Zeo? If you meant that it didn't do a whole lot to prevent RTN then I would agree, I tried in vain to use Zeo as a mechanism to prevent inexplicable SPS losses but it did not make a difference. Water looked fantastically clear and PO4 and NO3 were completely zero, but coral losses were exactly the same before and after.
Unfortunately this is the nature of SPS. Sometimes they just kick off for no apparent reason.
Hope that it's just the one colony for you and not a 4 year nightmare like what I've had to deal with (I wouldn't wish what I've been through on anyone!!)