You should definitely inform your husband when you become niddah (“I am niddah” or ” I got my period”). If you are spotting beforehand, you can tell him that you are not niddah yet, but you probably will be niddah soon.
As far as the taharah process is concerned, some couples feel comfortable discussing every step of the process. Others prefer that the wife just let the husband know when she expects to immerse. You and your husband can discuss what level of information and involvement feels right for the two of you. This is also an opportunity to discuss the logistics of mikveh night, such as who is watching the kids if relevant.
Upon returning from the mikveh, you should let your husband know that you are tehorah.
Please feel free to get back to us with any further questions.