The Ceralpha Alpha-Amylase reagent (R-CAAR4) can only be used in the pH range 5.0-6.0, as stated in the data sheet.  To assay amylase at pH 6-7 you will need the Amylase HR reagent (R-AMHR4) which contains a thermostable α-glucosidase and allows assays to be performed at temperatures up to 60°C and over the pH range 5.2-7.5.  This reagent is sold separately (R-AMHR4) and is also a component in the Ceralpha Kit (K-CERA).

Product Page (R-CAAR4)