Fluid head height and foam/gas level control apparatus associated with a primary reaction chamber of an effluent processing electrocoagulation assembly is disclosed. The apparatus includes a plurality of rotatable disks each having an orifice located therethrough toward an outer circumference of the disk. The disks are mounted in a horizontal array of openings located at an upper portion of the primary reactor chamber, the orifices communicating through the openings, height of the orifices in the chamber being selectable by rotation of the disks. Rotatable restrictor plates are mounted on the disks for selective restriction of flow through the orifice.