It takes about 3-6 days for the bait to kill slugs.  Putting down a beer trap will catch slugs. Putting down a wet newspaper or paper towel and removing it in the morning is another way to remove slugs.
Slug damage is usually limited to holes in leaves and slime trails. Are you monitoring soil moisture before you water. Some die back is also expected after shrubs are transplanted. First they sleep, second year they creep and the 3 rd year they leap. The shrub on the right also looks like it has rabbit damage. Some of the branches have been clipped  and leaves nibbled along the edge. 
The hydrangea on the right is definitely struggling but I suspect a root problem. Careful watering is probably what it needs. The one on the left looks great so it was probably weaker than the one on the right when you bought them, because the on on the left looks great your care must be excellent.