Developers intended for Photofinishing use are often suplied as "replenisher" and "Starter" the user mixes up a batch of replenisher, and then adds the "starter" to the mix. The starter has some Bromide and a few other things to ballance out the tank. (photofinishing is normaly done is processors that use several Gallons of developer.)

the tank is then replenished, and the starter is only used again if a significant volume of developer is replaced.