How long does hypo last

I know, of course, that mixed hypo will deteriorate with use AND that it will deteriorate over time if left in a dish, but how long can it be mixed and not used before it needs to be discarded?
I ask as I sometimes only make a couple of 5x4 salt prints in 3 - 4 hours. Should it be discarded after x - hours?

not all hypo is the same.
also depends on usage.
the kind I mix lasts for months

Until it goes out. That is why there is hypo test. Or it takes twice as long to clear film as it should.

It depends on whether the fixer is acidic or not. Hardening fixers which are acid have a shorter life span than neutral or alkaline ones. If you are using a "plain" hypo bath it depends on whether it contains sodium sulfite as a preservative or not.

ColinRH said:

I know, of course, that mixed hypo will deteriorate with use AND that it will deteriorate over time if left in a dish, but how long can it be mixed and not used before it needs to be discarded?
I ask as I sometimes only make a couple of 5x4 salt prints in 3 - 4 hours. Should it be discarded after x - hours?

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Tetenal sells hypo test strips,which indicate how saturated the fixer is with silver salts.after 1-3g/l, it's time to mix fresh.unused fixer should be good;see the hypo test above.time to clear a film striptimes 2 is a good starting point;so are the manufacturer's recommendations.

Thanks all for the information.
I am using straight hypo for salt prints and for fixing PMK negs. Easy to check the negs hypo but for the prints it seems a visit to Tetenal is required.

I use straight hypo for prints - just sodium thiosulphate and water - often. Nothin' else in the mix. Supposed to die fairly quickly, I've found it keeps for a very long time.

At the beginning of a printing session, I test the fix. Under safelights, I bend a strip of paper into sort of an "A" and hang it in a tray or small graduate of hypo, and fix for 3 minutes. Then I turn the room lights on (which exposes the paper), and put the whole strip in a graduate of developer.

If the fix is good, the fixed portion of the paper will be pure white - if the dev. is good, the unfixed portion will be dead black. For long print sessions, I'll do the same test several times to be safe.

I do test every keeper print for residual silver and for residual hypo - I leave enough margin for the drop tests so it can be trimmed off (even on properly fixed and washed prints, the droplets of tester will turn yellow or brown eventually).