I dont understand what happend. Ive had this colt for 6 months, it was growing and thriving at a whopping 8x10+ inches, then all of a sudden within a few days its dead

I noticed about a month ago when my clowns started to host in it, it shrunk down a bit, it was still open but just a tad smaller, so not sure if i should blame the clowns?
but there were alot of things i did different in the tank the past month
1. i changed salt brands
2. i started dosing with c-balance
3. i bought new corals, including more colts, shrooms, toadies and a hammer, all appear healthy
I added c-balance for the first time about 6 days ago, i added 11 tsp of each bottle for my 220 gallon tank. all corals looked great except i noticed the next morning my colt had goo all over it.
i pointed the
power head towards it to blow off the goo, which it did blow it all over my other corals

i tried to net out what i can get but its kinda hard in a larger tank.
the next day half the colt was turning to mush so i cut off at the stem all the dead parts. 50% of the colt still looked good.
the next day that side was turning to goo and was a goner. i couldnt remove it because it glued itself on several rocks. i tugged a little but it wouldnt budge and my rocks were starting to shift, i got scared and stopped tugging. after all this is a bare bottom tank and i didnt want any avalanches.
so just now i cut it off with a scissor, still underwater in its spot, i had no choice. bits are flying everywhere
today i will do a water change and add carbon
in its path it took out my cleaner shrimp

may he R.I.P
my toadstools are closed now and im really worried
and the worst part is i have 2 other colts in the tank! they are fine but i dont want to go through this again...no more colts!!
well now i have to fill that enormous empty spot left by a sudden death
heres the colt about 6 weeks ago, right before the clowns started hosting in it
