Hello Oliver,
You should use the solution exactly as described by Christoph Caspari for preparing it yourself, following the dilution instructions on the bottle:
http://www.fotolaborinfo.de/fotolabor/fsas....htm#Waesserung
Oh, and one more thing: the working solution is for single use only. Use it and then pour it down the drain with a clear conscience.
You can, of course, still apply a selenium toner afterwards. The rinsing aid makes the rinsing process easier, whilst subsequent toning or rhodanide (trade names Sistan or Adostab) at the end improve the stability of the silver image.
Best regards,
Franz
