The crystals grow from a saturated copper sulfate solution, which means they grow from a solution made by dissolving as much copper sulfate as possible in water. Make a crystal growing solution by dissolving as much copper sulfate (cas No.7758-98-7)as you can in hot water. You want the water to be hot because more copper sulfate dissolves in hot water than cold water. If there is undissolved copper sulfate at the bottom of your container, it's ok! You can pour the saturated solution through a copper filter to separate out the solids. You want to keep the translucent blue liquid.