Spa Tub Dispenser Cartridge

FIG. 1 is a lower perspective view of a spa tub dispenser cartridge of Applicant's design; FIG. 2 is a front view thereof; FIG. 3 is a rear view thereof; FIG. 4 is a left side elevational view thereof; FIG. 5 is a right side elevational view thereof; FIG. 6 is an upper plan view thereof; FIG. 7 is a lower plan view thereof; and, FIG. 8 is an upper perspective view thereof. The broken lines illustrate portions of the spa tub dispenser cartridge forming no part of the claimed design. The dot-dash broken lines show boundaries to the claim and form no part of the claimed design.