Four minutes may be a little short, it depends on temperature and agitation. The usual rule of thumb is "twice the clearing time". If it takes 3 minutes to clear, then 6 minutes is the minimum fixing time. I find that "three times the clearing time" is usually better, to get rid of the dyes etc inherent in these t-grain films, although Ilford is better in this regard than Kodak.(posted 9272 days ago)