Amanos, h202 and manual removal will work the best for getting rid of it. I've had a little bit of luck using a toothbrush to snag it out.
Spot treatments work best with H202 but maybe in your case you should do a standard dose for the whole tank.. I've heard lots of different opinions about how much to dose, i'd say 1ml for every gallon, once a day for a few days, any higher than that and it will probably screw up your plants and livestock. Cannot recall how the bio-media handles h202.
I've used h202 to rid my tank of spirogya in the past, just a light dose for a few days and it all dissappeared, the rhizoclonium should react similarly.