A flocculation apparatus and method for treating colloidal suspensions. The apparatus includes a suspension inlet, a suspension outlet and an inner cone mounted centrally in a conical outer housing. The inner cone and/or the outer housing is rotatable relative to one another and a gap for through-flow of suspensions is present between the inner cone and the outer housing. In the method, continuously measuring a flock size distribution of a suspension stream passed into the flocculation apparatus is provided. Additionally provided is axially displacing the inner cone and/or outer housing as a function of the flock size distribution and the suspension volume flow rate.