Yes, the tang will eat it.
No, caluerpa does not always survive well being cut. Macro algaes aren't plants, but still unicellular algaes. Cutting them can kill them.
They will help to lower nitrates, but SLOWLY.... Macro algaes are not a "cure all".
Shista, GET A BOOK!!! You've got to research stuff on your own before you make decisions to "get" things.