Hello im still new to marine fish keeping i have a 90 gallon tank with 2 canister filters and i try and add some new fish but every time i do one or two of my old fish dies.i check the water parameters and there fine. I have a airstone to help produce oxygen and i think ive got a good amount of hiding spots i just dont understand and can’t really find anything about it. If i could get help i would greatly appreciate it.