The ornamental design for a koipond floating plantprotector, as shown and described.
FIG. 1 is a top, perspective view of a koi pond floating plant protector showing my new design;
FIG. 2 is a top plan view thereof; and,
FIG. 3 is a side elvation view thereof.
All sides not shown form no part of the claimed design.
The broken lines showing the plant root container and the net hanging down to the plant root container are for illustrative purposes only and form no part of the claimed design.