What is disclosed is an apparatus and method for inhibiting the formation of sediment in an ink sub-tank of a MICR inkjet printer. In one embodiment, the present apparatus comprises an ink sub-tank containing MICR ink substantially comprising a ferrofluid of particles, and an electromagnet. When the MICR inkjet printer is turned OFF, the electromagnet is lowered into a chamber inside the ink sub-tank and an electric current is applied to activate the electromagnet. Activation of the electromagnet causes the particles of the ferrofluid to be attracted to the electromagnet's magnetic field such that the particles are lifted off a bottom of the sub-tank to inhibit sediment formation thereon. The electromagnet is de-activated when the MICR inkjet printer is turned OFF. A sensor is employed to activate the electromagnet when sediment in the ink sub-tank has reached a pre-determined level.