Wonder Shells are a product that helps stabilize your Freshwater ph
(7.0-7.6), add Calcium carbonate (which is beneficial to even low ph
fish such as discus), and add minor and trace elements (electrolytes).
They are beneficial for African Cichlids, Livebearers, goldfish, some
plants, and even Discus. Wonder Shells also remove chlorine. I
personally have used them for years; they are NOT a new product, but a
tried and tested product.

http://www.americanaquariumproducts....nderShell.html