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I never had any of the usual ways work for me. I would either place a frag tile next to a colony that the colony would quickly attach to, at which point I simply removed or moved the tile. The other thing I did was to remove the Xenia and place it in the lower flow fuge for it to attach to rock rubble.
Go with white pompom Xenia (aka pink Xenia) not the regular. It is not quite as virulent, stays shorter (not long stalks that flop around), and almost never stops pumping.