Decreasing Fluoride in Water Wells with Resins

In the  region of São Paulo I have several clients with the problem of high fluoride ( 3 to 5 ppm) while the Brazilian legislation allows the maximum of 1.5 ppm. The water comes from deep wells between 150 and 300 meters. In one of them, I am testing a solution implanted with anionic resin ( 1100 l) activated with NaCl. However, the removal cycle is very low - 3 hours for approximately 30 cubic meters of water. Does anyone know the reason for such a low cycle? Is there any way to improve it? I know other anions have a preference and I believe this is one of the problems. For 70 m³ a day, what would be the most appropriate recommendation for 70 m³ a day? Is there a way to transform this "resin vessel" into another product of better efficiency?