Hi
I worked retail aquatics for 10 years in a specialist coral store and I would say many of the problems people experience with SPS & LPS corals are related to instability in alkalinity. Now years on we have far more 2nd 3rd 10th generation frags and colonies in the hobby so SPS tend to be hardier and more adapted and some are as bullet proof as it gets.
All that said whenever someone came to us with a problem if I dug into in forensic detal to what had been going on with the aquarium it always starts with all my parameters are stable blah blah blah Then you dig in with them and walk them back over the previous couple of months 7 out 10 issues would have been triggered by oh my Alk was high or low it could be 3 months past but there always seemed to be an Alk related issue in the mix then you would see an outbreak of brown jelly or stripping, mysterious loss of colonies etc etc.
I did this over 100's of tank and users over the years as much to understand what was going on and what we could learn.
These days the one parameter I always want stable is ALK, I have seen SPS corals happily growing albeit slowly with calcium at 250ppm and corals growing in 1ppm PO4 with Nitrate hitting 200ppm but if there are ALK swings then there is trouble ahead.
All anecdotal but thats my experience of ALK
