A large water change would be best, the tiny trace amount of iodine in the salt mix is not going to make the problem worse as it is in correct ratio/ amount needed.
There could also be other factor in play with your tank condition though without all the details and intimate knowledge of your particular system making a accurate diagnosis to many of our issues is not going to happen online. We merely can make suggestions and try and nail down a possible source for you to explore as the problem.
I once had a tank that could not keep Zoanthids / palys of any kind as they would melt down in a matter of hours after being introduced into my tank.
All parameters were fine as far as test kits could tell, All existing SPS LPS and softies were thriving well and to this day I can not come to one certain conclusion as to what the heck was going on in that tank.
Today I am still employing the same methodology, maintenance, same salt brand and source water as I did back with that particular tank and I can keep such things now without any issues and they grow well along with all the other types of corals.
The only thing to date that I still can not keep is Xenia species for some weird reason, which I am fine with of course, it melts away just like the Zoa/ palys once did in the previous system.
Some say its from nutrient deficiency in my case with the two cases/ instances though I have for a long time now kept any system I maintain with a healthy balanced No3 and Po4 level, keeping all my corals healthy.
So the short of this is that while you were dosing something in likely excess without testing, there could be other reasons for your unfortunate mishap.
I would do 50% or more water change making sure that the SG, Temp and DKH levels match the current tank parameters before changing the water and this should give the corals the best chance at rebounding or salvaging the ones that are not too far gone.
Hope your tank pulls through without a total disaster,
Good luck and happy reefing
BluewaterLa/ Mike.
PS. you are correct that ALL of us make some bad decisions from time to time and even some bone headed mistakes. When it comes to this its like everything else....
There is those that have and those that will eventually.
