Fixing process is sensitive to temperature and agitation. I give most films continual agitation for at least 5 min at 20C or slightly above in rapid fixer containing 100-120g/l of ammonium thiosulfate plus some sulfite and pH buffering agents, roughly comparable to Ilford Multigrade Fixer 1+3 to 1+4. In a fixer like Ilford Multigrade Fixer it's very hard to overfix.(posted 8157 days ago)