I have a stock of Kodak Rapid Fix that contains a separate bottle of the hardener solution... now the questions:
i) For paper can I leave out the Hardener when I mix up a working solution?
ii) Do I just substitute water for the missing hardener volume?
iii) Any changes to the fixing times or capacity?
The hardner is really intended for film, so leaving it out for prints is OK, and likely eases various toning processes. I see no need to make up for the lost volume from leaving the hardner out of the solution. And, fixing time and capacity should remain the same without the hardner.
I use the hardener for film but not for paper. I just mix the fixer to a 1-gallon capacity without the hardener. I guess that means I use water to replace the hardener volume.
I mix paper fixer without hardener to film strength. I use a two-bath fix for fiber paper and go 30 seconds in each bath. For RC paper, I use a single fixer bath for 30 seconds.
I do not use hardener with either B&W film or paper. I do not need hardeners with the film/developer combinations I am using. Most (but not all) of my film developing is done with staining & tanning developers (like Pyrocat-HD). For film I use a single bath in a non-hardening alkaline fixer (like TF-4). After fixing I do a water rinse followed by a short soak (about 2-5 minutes) in a 20 gram/liter solution of sodium sulfite dissolved in water (a washing aid). Then I do a multiple water change final wash.
It is important to remember that fixer (other than fixer on the surface) is removed by diffusion so soaking in several water changes is a very efficient way of washing both film and paper.
Virtually all of my printing is now Azo Contact printing and hardeners are a no-no with that process. I use a 2 bath fixing process followed by a short soak (about 2 minutes) in a 20 gram/liter solution of sodium sulfite dissolved in water (a washing aid). Then I do a multiple water change final wash.