They sell an aquatic version of glyphosate for pond use. Not sure if the formulation is different or it is just price gouging.I've been told round up will kill it.
sprayed ours couple years ago with copper sulfate, hand sprayer tank from boat. Sprayed tops of the matts of moss. Ours was mostly along shoreline to 20 feet out. did 1/2 pond then other half a few weeks later, killed it and pond has been clean so far.