Complex sentence: Cationic softeners are incompatible with anionic surfactants presenting the bulk of surfactants used in detergents, with which they form inefficient precipitate; therefore they cannot be mixed with the detergent, but have to be added during the rinse cycle instead.
Split into simpler sentences: Cationic softeners are incompatible with anionic surfactants used in the bulk of surfactants used in detergents, with which they form a solid precipitate. Therefore, they have to be added during the rinse cycle instead.