Per the product label: Vexis Herbicide Granular Label 2lbs per 500 sqft is accurate.
How to Calibrate your Spreader
Vexis Herbicide Granular is not labeled to control clover. Clover is best treated when it just emerges as once it flowers it is almost impossible to kill. Atrazine is always on an option for St Augustine. Weed Free Zone is another option if you do not have floratam or bitterblue variety. Depending on the type of clover you have a pre-emergent like Gallery is a great option to prevent it coming up. We also have helpful guides here that can help.