Flow controller including a flow control chamber, a diffuser and a fixed-length stop. The fixed-length stop includes a stem and a plug. The stem can be compressed along its longitudinal axis. The flow controller further includes an interface that detachedly affixes to the flow control body. A fixed portion of the fixed-length stop is affixed to the interface. The flow controller further includes a plurality of fixed-length stops with a number of predetermined lengths. When installed, each of the fixed-length stops is positioned a predetermined distance into the diffuser to produce a certain flow rate of the fluids passing through the flow control chamber. The fixed-length stops are color coded according to the predetermined lengths.