Quote Originally Posted by Tofek View Post
But it is written on the box that you can add it to a stop bath, so basically just an acidic solution, nothing more, right ?

Do you use another type of hardener ? I read about a formol based one.
The Tetenal Harter is an alum based hardener. Alum must be in an acidic environmento to work properly.
So basically yes, you can use it also as a stop bath.
There are other hardeners available: formaldehyde, glutaraldehyde, chrome alum...