Kodak F-5a

Water, about 125ºF (50ºC) - 20 fl. oz. - 600mL - 25 fl. oz.
Sodium Sulfite, desiccated - 2 1/2 oz. avdp. - 75g - 3 oz. avdp.
Acetic Acid (28%) - 7 1/2 fl. oz. - 235.0mL - 9 3/8 fl. oz.
Boric Acid, crystals - 1 1/4 oz. avdp. - 37.5g - 1 1/2 oz. avdp.
Potassium Alum - 2 1/2 oz. avdp. - 75.0g - 3 oz. avdp.
Cold Water to Make - 32 U.S. fl. oz. - 1.0L - 40 Imp. fl. oz.

U.S. Customary and metric measures given are exact. Imperial measures are accurate to within 1/16 oz. avdp, with liquid measures being exact in the proportion of 4 U.S. fl. oz. : 5 Imp. fl. oz.

If it is desired to mix a stock hardener solution, use Kodak F-5a, adding one part of cool hardener to four parts of cool 30% hypo solution--2.5 pounds (3 pounds if Imperial rather than U.S.) of hypo to the gallon of solution.

Same question as the other two formula you posted.

Why?

I'm not tring to get on your case, it just needs some explanation for me to want to try it is all.

The information is in the Kodak publications.

Why does it have that bit about a stock hardener ? F5a is an acid hardening fixer.