New fish dying. Old fish ok.

Question
I have had a 35g fish/invert tank established for 5 months now. Shortly after cycling I added a Midas Blenny, Lawnmower Blenny and two Clowns. Also Sally lightfoots, camel shrimp, tuxedo urchins, purple lobster and to this day they are doing great. On and off for the past couple months or so I have been trying to make new additions and nothing will survive. I've lost 2 angels, 3 sets of damsels' two spotted goby and a butterfly fish. My question is I why are the first additions doing well but everything I've put in recently not surviving? My wate quality is great. I have a nice fugue with a sock filter so I would say water quality isn't the issue but I'm not an expert lol. It's trivial because the successful fish swim in the same water as the ones that have died. For example: my lemon peel angel survived over a week and was eating well. He looked real happy but this morning I woke up to him floating. Sometimes they'll show disoriented behavior ect. like usual stressful behavior and sometimes die without warning. None have laste dmore than a week or so. Could I be not acclimating them right? I figured if thAt was the case they would die faster.... I understand a fish may die but this is getting quite expensive lol. Any help would be greatly appreciated. Thank you.

Answer
first off, your tank is fairly full so i would suggest adding no more than 1 fish. i know it is always tempting at the lfs to buy the prettiest fish, but the prettiest fish are almost always the hardest to care for. such as your butterfly, butterfly fish are very very delicate, expecially with your clowns which are no doubt aggressive beyond belief when it comes to new additions. to avoid this i would suggest switching around the rockscape and switching the lights off after each new addition, this will help for a bit but the clowns will eventually become very protective of their territory which will take up most the tank, so if things dont get any better you may want to thinka bout trading them in.

i would not suggest adding any more larger fish, the two angels and the butterfly will all really outgrow that tank, especially with the other fish in the tank. i would suggest a 55 or larger for fish such as these. also they will nip at corals if you have any.

also this all could be due to acclimation process, alot of times a very extensive acclamation process will do more harm than good. with fish i usually just float the bag for fifteen minutes and gradually fill the bag with tank water to get him used to it. i would suggest a far more drawn out process for corals however.

if you decide to add any more fish i would suggest just getting another little cheap one, maybe a cardinal or something just to see how things go.

hope this all helps you!
i would suggest waiting a bit before adding another fish, and dont forget to not overstock the tank!