Purple bonsai small issue

[HB AL]

I have a nice colony of purple bonsai and noticed a couple weeks ago a small zone where it was entrusting but starting to shoot up small shoots,where it looked like algae growing or something. So I took it out dug out the small dead zone and gave it an iodine dip. Did this about 4 days ago, 2 days later a small fully encrusted frag of it from a few months back had died overnight. I have hundred of corals mostly acros and this is the one with the only issue. The frag that died was probably 2 feet away from the mother colony, any ideas welcome. Thanks AL

 

[DesertReefT4r]

Not looking good. Frag what healthy tissue you can.

 

[HB AL]

The frag is toast the colony is fine let me get a pic with the kessils turned too all white. Algae growing where death occurred, no new white death zones since scraping and dipping.