I've made plenty of mistakes over the years, especially with fish. To me, corals are pretty easy - keep the water up, light and place 'em right, and you'll do okay. But fish are a different matter. I look at my corals, but I interact with my fish. They also interact with each other, and all have personalities, as anyone who's kept them knows.
I'm sorry to hear of your bad experience with ATR and the fish you chose. Lions are great fish for their beauty and agression. A top pick for a predator tank IMO. How frustrating to have been told that a lion would get along with the other smal fish you already had and the new ones you purchased. How frustrating to see them die. How frustrating to have stressed your tank further by catching the lion to get him out.
It would be nice to assume that the LFS would provide you with good information about stocking your tank. Sometimes they do; sometimes they don't. It really goes without saying that you learned from the experience.
Over the years I've heard and read about so many folks having problems with fish in their tank. It's usually disease or predation. I've also heard and read so many remedies and approches to addressing such things when, in reality, stocking is the key.
Stress kills fish. Too many or the wrong combination of fish in a tank creates stress. Fish define the heirarchy in a tank, not the aquarist. Disease and predation are all kept in check when reasonable stocking selections are made. IME, any tank 90 gallons or less has room for ONE dominant fish. ONE. Any more and trouble ensues. Additional fish can be added, but care should be given about how the new fish will interact with the dominant member.
I've run salt since 1985. My current reef is nine years old. The dominant fish is a Sebae clown that is an original occupant, so he's nine years old plus whatever he was when I got him. He tolerates two blue chromis, a fire fish, and a yellow goby, all of which are over five years old and extremely healthy. I take pride when my specimens live long lives. I hope other aquarists do as well.
When it comes to HA, I'm not quite so savvy. LOL
Good luch with the hobby. :rollface: