The best replacement for copper sulfate is copper chloride.

The best alternatives to copper sulfate are rated as following:
★★★★★  copper chloride
★★★★  copper gluconate
★★★  rock salt
★★★  cupric sulfate
★★  foaming root killer
★★  cutrine
★  dichlobenil
★  copper hydroxide
★  rootx

Your alternative for copper sulfate is not listed? Suggest!
Speaking about copper sulfate, one probably shouldn't forget about zinc.

Other search terms related to copper sulfate and their ratings are:

★★★★★ zinc
★★★★★ ammonia
★★★★★ sodium hydroxide
★★★ aluminum
★★ iron
★★ potassium iodide
★★ iron reaction
iron nail
sodium carbonate
steel wool
You have in mind a companion for copper sulfate and it is not yet here? Propose!

Google Trends

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copper sulfate
copper chloride
copper gluconate