Thanks Mr Bill,
Yes I'm mixing from Chemical components.
I've been developing B&W with success (although I didn't mix my own developer)
I'm using a Patterson tank employing a Hot Tap method for temp control (I'm pretty sure I got that part right)
Your comment on the fixer has got me thinking....I was unable to source Ammonium Thiosulphate and am using Sodium Thiosulphate instead. I understand this is much slower and having no idea how much to use I began by adding small quantities and testing the fix time using off cuts from film ends. Eventually I ended up adding about 80g of the Sodium Thiosulphate and still had a very long fix time (Close to 10 minutes!)
I don't know if anyone can shed light on this any further. Perhaps I should increase the quantity of Sodium Thiosulphate even further?