A number of different factors can be responsible for ink foaming: The type of development unit, brush pressure, number of brush rotations, condition of the brushes, supplier of the chemicals, age of the chemicals, air pressure, outdoor temperature, filling level of the tank or pressure on the spraying tubes.
If no machine malfunctions can be detected, then the addition of an antifoaming agent such as Agfa RC 31 is recommended. Please remember not to exceed the recommended quantities, since it can otherwise come to ink receptivity problems.