ok so i had a couple of fish and for some reason in my tank the same species keeps dying while the less hardy ones are living. i had about 5 chromis they all died, i had 2 blue damsels they both died and the ones that stayed living are all the coral, a firefish, an achilles tang, a yellowtail damsel, and a bicolor cleaner wrasse. all my parameters are perfect thats why i dont understand why they died. i even tried getting them from different stores too so it cant be the provider that has bad fish and they dont have any deceases or ich.