Thanks for the comments guys, appreciate the input from everyone.
Not sure I really want to tell anyone what I did to stop the aggressive death toll that was going on inside my tank. Definitively DO NOT TRY THIS ON YOUR TANK !
Really.
After the odd fish loss I=and seeing strange spots on my Gem tang I had had enough.
Convinced that I was dealing with a tank wide bacterial infection I decided to treat with antibiotics. Nothing from the LFS though, something much more interesting.
I dosed 4 pills in total of Antibiotics given to a 100lb dog. It likely wiped out every bit of good bacteria as colours browned out soon afterwards and my skimmer continued to go crazy
I dosed one pill each day for 4 days, ground up into a fine powder and mixed well in a salt water slurry.
Results were easy to see and happened very quickly.
Not a single SPS RTN since the final dose. No fish loss since the dose.
Have several pieces that are still very slow STN but that is likely from the corals being so stressed out.
Lost many, many collector pieces and prize specimens but others have survived. Including my Orange passion which I am happy about.
Several frags of pieces I lost are plugging away in the frag tank, hopefully they keep on keeping on. Red planet, red dragon, Kryptonite torch and others.
So to sum up.
I havent given up
My tank is much lighter

and I have space for things to grow in and maybe add
Will let it sit for a little while longer and start adding some new pieces back in
Thanks for listening
Dwayne