If you have a DSB no you do not have to clean it.
If you have CC, yes clean it or you will have a nitrate factory.
argonite(sp) takes many, many years to dissolve, many years. It dissolves under a low oxygen area in the sand bed.
If you have to add it their are many threads on the board and many ways people have done it. I would try a search first if you haven't.
good luck.