I claim an ornamental design for a solution monitoring apparatus, as shown and described.
FIG. 1 is a perspective view of a solution monitoring apparatus;
FIG. 2 is a front view of a solution monitoring apparatus;
FIG. 3 is a side view of a solution monitoring apparatus;
FIG. 4 is a side view of a solution monitoring apparatus;
FIG. 5 is a top view of a solution monitoring apparatus; and,
FIG. 6 is a bottom view of a solution monitoring apparatus.
The dashed lines of the projectile and/or components thereof and unshaded areas within the dashed lines are for illustrative purposes only, and form no part of the claimed design.