First, the HCA /thiosulfate/rapid fix question:

All fixers contain thiosulfate, except some very special ones which are truly nasty. So the thiosulfate is what does the job.
There are two forms of thiosulfate used in fixers: Sodium thiosulfate and Ammonium thiosulfate. The sodium (Na) version is called "hypo", the ammonium fixers are usually called something with "rapid" in it. The reason for this is that the ammonium actually sppeds up the rate of dissolution of the silver halides. Since this is a function of the ammonium it's not specific to "ammonium thiosulfate". You get the same effect by ading a few teaspoons of ammonium chloride to a liter of Hypo fix - clearing times down to less than 20 seconds.

Fixers are either acidic or alkaline (and some are almost neutral). Alkaline fixers wash out more rapidly. When using acid fixers, HCA will neurtalise the acid and make the film (or paper) alkaline - thus washing out faster. The HCA also helps converting some of the byproducts of fixing to more easily soluble compounds. Due to the more rapid washing after alkaline fix, this is not necessary unless using acid fix - or very old fix. If your fix is yellow, it's dead. If it gets really bad, it will work as a hypo toner - although not as cleanly.

Don't worry about the life expectancy and capacity of the fix: If in doubt, make new. Compared to film, fixer is dirt cheap: Don't risk it.

Phenidone is not very stable in solution: Measure new every time, a per cent solution is very unreliable.


Sodium bisulfite and sodium metabisulfite have different formulas, but are thought by many to be the same chemical. They are certainly interchangeable.


Pyrocat-HD: Instead of making a solution "B", I dissolve the equivalent amount of carbonate in the mixing water. For 1 liter of 1:1:100, use 6.5g of sodium carbonate monohydrate, or 7.3g of potassium carbonate. Dissolve in 1/2 liter water, add part A dissolved in the other 1/2 liter.


Amounts: I suggest you reduce your KBr to 50 g, and buy 200g Hydroquinone. It's not used in Pyrocat-HD, but it is a very useful developing agent to have around. Some (250g?) Metol is useful to have, as well.