Tank transfer didn't go well

[GreenSpottedPuffer]

Well it didn't go well at all. I have the worst luck with transfers

So I simply moved everything over in old tank water two nights ago. Added 5G at a time of newly mixed water (mixed for a full day in advance). It ended up being about 40% new water that was matched for salinity, temp. and alk. I have done water changes this big before, so thought it wouldn't be a big deal.

I rinsed out some sand in old tank water and added that. Really not much at all. about half the tanks bottom is bare. I just want a bit for looks.

Everything seemed to go really well but the next morning, three of my nicer, big sps colonies were either completely dead or receding. Then this morning I noticed a gorgonian is dying and also my birdsnest is dying. The birdsnest is kind of loosing flesh in random spots This one kills me because its one of my favorites.

Everything else looks really good though. Makes no sense to me