The present disclosure includes mixing apparatuses comprising a first conduit defining an inlet channel, a second conduit defining an outlet channel, and an injection assembly that is disposed between the first and second conduits. The injection assembly can comprise two or more mixers, each having a reducer conduit that defines a mixing channel and an expander conduit that defines an expanding channel. The injection assembly can also comprise a first injection conduit configured to inject fluid into the mixing channel. At least one of the mixers can comprise a shut-off valve movable from an open position to a closed position in which the shut-off valve prevents fluid from flowing from the mixer to the second conduit. Closing the shut-off valve can increase the fluid flow rate in at least one other of the mixing channels.