The growth rate of any aquatic plant is normally in proportion to its ability to utilize nutrients. In other words, any plant that has a high nutrient conversion rate is likely to be a rapidly growing plant, maybe even invasive.
Tilapia will help eliminate the FA problem, but will have no perceptible effect on the nutrient load.
Have you considered somehow diverting the cattle pasture run-off? Seems like the only sure fire solution.
