If you've only got FA around the edges of the pond, you'd be pretty safe to try fertilizing again without further application of the Cutrine. The FA in the five-acre pond I work with was forming some pretty extensive weedbeds that ranged out into water six feet deep and more when I fertilized the first time, and within a week after fertilizing the FA was a distant memory.
The fertilizer won't hurt in the slightest as far as eating the fish; the same chemicals used in pond fertilizer, nitrogen and phosphorus, are routinely used for fertilizer for agricultural crops. Copper sulfate is approved by the EPA for aquatic use, so one application won't hurt anything, but I wouldn't use it too regularly.
