I have used Algaefix before. It's moderately effective, but it doesn't treat the source, and yes it WILL affect your macros some. No they won't die off altogether. Neither will the HA.
Check your bulbs....if they're close to a year old you may want to replace them. Cut back on your feedings, and consider using a GFO. Your phosphate readings are in the norm because of the algae soaking it up...macros included...but something is clearly feeding the system.