Correct, the vegetation and the FA will utilize the fertilizer before the bloom can get established. I think that if you add more fertilizer you will see an increase in FA for sure, and possibly APW.
I've noticed in ponds that had vascular weed growth, that the amount of weeds inversely corresponded to the amount of FA. (more weeds, less FA) Also, the ponds that have FA and submerged plant growth have higher secchi readings (clearer water).
In ponds where the FA and submerged weeds are severely curtailed (with the use of chemicals) a bloom is easily established. But, if rooted plants can get to the sunlight and grow (like APW can), then the bloom receeds as the plants increase in number. Also, FA usually gets it's start by growing on the bottom of the pond; it needs sunlight to do that. Even with a strong bloom, it can grow in <24" of water. The same chemical that knocks back the FA, also restricts the bloom from getting established. So it's hard to control FA while at the same time keep a good bloom going. Not impossible, just hard.
I've had good success in either getting Tilapia in a pond before the FA gets out of hand, or chemically knocking back the FA, then immediately introducing Tilapia so they can keep the FA pruned back while the bloom gets established. That way, all the Tilapia have to do is eat any FA that is <24" deep or so.
