Couple of points here -
The procedure to turn on the anti-ice is 2 fold.
1/ You may have inlet icing in the first instance.
2/ Relieve the pressure downstream by using the anti-ice as a secondary manual bleed valve.
Pay attention as to when to use ant-ice. Less than 5 degrees C and "visible moisture". The key being visible moisture. i.e. if you can see a cloud is a start point. If it is less than 5 degrees having the anti-ice on is no issue for performance.