Actually I think it is because he is too young. "Herman" is much less sour now than he was six months ago. Feed him and split him a few times, even if you throw away the split, it will be worth it in the end; We hardly ever use Yeast now (except for pizzas).
Thanks for the info, I have taken 2 cups out and added 2 cups of flour and warm tap water, I've also split him up so he has more space, the acrid sour flavour hass been tempered. I may make a loaf tomorrow
I use a BBC recipe, http://www.bbc.co.uk/food/recipes/sourdough_starter_22976 but since last Saturday used RAW (unpasteurised) milk as an experiment. The starter turned out OK and not smelly but the final bread was wonderful. Instead of a dusty grey/brown (as in Waitrose), this bread looked a golden yellow like Victoria Sponge and what's more had more air pockets than usual.