Catfish Dying

[Corykeeper]

Over the past week I have had 2 brand new emerald cories die and a bushynose pleco die. they all were acting normally until I come back from classes to see them keel over. all the other fish seem relatively unaffected. The bushynose also died in a separate tank, both tanks have good water parameters. Does anyone know what it is or how to handle it? 

 

[Ch4rlie]

Is your tank cycled first of all?
 
and need size of your tank?
 
And also water test readings......