It depends where the FA is. If it's in water less than 24" deep, Cutrine Plus Liquid should do a number on it if it's applied according to the label.
If it's FA in water that is deeper than 24", then use Cutrine Plus Granules according to the label.
If you don't kill the FA, it will explode if you add fertilizer.
If you can't use Tilapia, then maybe a combined chemical/mechanical removal plan is an option too.
FA grows because of excess nutrients. If you can get the FA knocked back enough, I'll bet you will see a bloom get established. One other thing. Have you checked the alkalinity and pH of the pond water? That could be limiting the bloom too.
