Atrazine does not stay around long enough to be useful as a preemergent in sandy soil. Never mind what a bad idea it is in a place that rains over an inch per day just about every day half the year. I deal with lots of zoysia in a climate that is similar to, but not identical to southern Florida. My experience has been that zoysia does best if it is not starved, mowed low with a reel mower every 3-7 days and neither allowed to dry out nor drown. Many weed problems in a zoysia lawn are fostered and perpetuated by mowing too high combined with starvation. Once that is addressed, Celsius is a good herbicide for many grassy and broadleaf weeds. Certainty is good for sedges. Three Way type products have not really impressed me. I am more impressed with metsulfuron as a broadleaf herbicide. 2,4-D ester or Speedzone Southern is something I use as an adjuvant for the above herbicides. As for preemergents, I have applied Gallery for persistent infestations by broadleafs and moderate rates of Dimension for grassy weeds emerging in the winter-spring months. The main preemergent in zoysia should be regular low mowing and maintenance of good fertility. In a sandy soil, a good practice to consider would be annual topdressings with finely screened organic matter until properly fertilized turf starts generating its own organic matter.