I have just received a reply from my resin supplier which explains all things :-
"As for the resins becoming black, did you observe any sticking blackish material in the resin. This may be due to bacterial growth in the resin, if kept stagnant in normal water. One needs to flush the water in the resin bed (only) everyday and replace with fresh water."
This I know he did not do as his DI vessel is linked direct to his water tank and hence there will always be static water. In this case his system had not been used for a long time due to bad weather.
So there you have do not have stagnant water in your DI vessel, this explains why a lot of guys had problems with their resin. Also at that time there was a lot of humidity in the air so any non sealed bags the resin would degenerate.
Doug