Pacus are eating more

Pacus are eating 20kg  of algae and the game only counts 10kg of this material, for example, if the pacu ate 140kg of algae he should produce 70kg of polluted dirt(this is what the game say, the pacus produce 50% of consumed mass), but really with 140 kg of algae one pacu only produces 35kg of pulluted dirt  ( 30 exactly, becouse pacus are producing 15kg of polluted dirt every 3 rations of  20kg of algae ( 3 rations of 10kg without bug))becouse when  pacus go to eat to a fish feeder and the fish feeder have 20kg or more, they eat 20 kg and count that like one ration, but if i put only 10kg in the fish feeder and i wait that the pacu eats the permitted 10kg  the game counts that like one ration to, and if i do this again 2 times more, after 3 rations of 10kg (30kg)the Paco produces 15kg of polluted dirt( 50% of consumed mass)