First I feel that the change in ph is enough to shock him really bad. But now that he has been in it for a week I would change it on him again. What is your temperature? If it is under 80 you might want to try raising it up a bit to get his metabolism going good. That can help make him hungry enough to eat in my experience. Keep the lights off in the tank, that will also help lower his stress. What does he look like? If he is all dark black then he is very stress out.