new aquarium need help*

hey guys I'm new to saltwater fish tanks and would like some advice. I have a 55 gallon tank with live rock no corals. in the tank I put in a spotted blowfish, yellow tang and long nosed butterfly about a month ago with no issues.two days ago I put in four clown fish all of the same species and today I found two of them dead. any ideas? I'm not sure what I did wrong and would like any help