I would let the tank settle if your losing fish. Second I would qt new fish to make sure they are good and don't infect your old tank inhabitants . I would recommend drip acclimation for new fish. I have done both and never any issues with just floating. Maybe they were sick from the get go, in a qt you can keep a close eye on them and see if anything goes wrong quickly and clearly.
Good luck and dont give up I have had many failure in the reef hobby and it is very rewarding. Have patience it will work out.
Try recalibration your refractometer and then test the water. It could also be that one of your fish is a bully and kills any new additions that haven't settled in.
