copper is not toxic in the doses you'd be using with plantex. I believe it has 0.001 copper or some such. I use it on my planted tank with cherry red shrimp and they're doing fine, and breeding as usual. The plants use it up LONG before it has a chance to accumulate or anything. Afterall, there is copper in the stream beds where a lot of crustaceans come from, just not in the concentrations that you'll find in the ick medications and things like that. (or with copper piping in a house and tank water sitting still with no plants) I wouldn't worry at all about the amount of copper in plantex though.