Will Crystal Plex hurt fish or animals?

Crystal Plex liquid copper sulfate and Copper Sulfate granular is safe for livestock, recreation, potable water and not harmful to most fish when used according to label directions. Oxygen depletion is the common cause for a fish kill. There are a few exceptions, Copper sulfate is not meant for small deco ponds and is toxic to Koi, Golfish and Trout.