A process to improve the polymeric filtration aid performance used in removal of gypsum from phosphoric acid/gypsum slurry. A synergistic effect has been observed by using a Dual Injection method. This method more specifically involves using two polymers (A & B) of different chemistry and injecting into slurry at a different time. The polymer chemistry of filtration aid A is selected from the group consisting of non-ionic, and anionic polymers and the polymer chemistry of filtration aid B is selected from the group consisting of sulfonated polymers. The polymer (A & B) usage is reduced by around 50% and performance improved.