In the ocean,the salt is one of the main reasons there is so much life there.Bacteria does not like salt.
At ..27 you have stressed fish as there salt removing organ is working hard,at ...25 you have ocean water,at ...22 you have the bacteria starting to be to strong for some inverts at this stage to have protection from the bacteria,also you have more relaxed fish at this salinity as there salt removing organ is not working hard.
at ...20 your inverts are suffering a great deal,but it is normally not a sudden death,unless salinity is lowered quickly,your fish if there are no external injurries are doing great.
At ...18 all none moving inverts are suffering and dieing and the algae in the corals as such is not doing well at all.
At ...16 you have what the wholesalers store there imported fish in (even lower salinity with some)to help keep away parrasitic attacks(white spot,etc).
The lower the salt the more avaliable oxygen,thats the only benefit in a marine aquarium.
When desperate,we lower salinity when the water is to hot to increase oxygen levels,but that still hurts the inverts,normally!