It's hard to completely eradicate them without stripping down the whole tank and bleaching all the ornaments and throwing out the gravel, which of course will leave you with an uncycled tank.
They are controllable, however. First, you need to feed less. Cut down your feeding by a third, and you'll see fewer and fewer of them. Second, wait for lights out when they climb up the glass, and scrape them off into a net and dispose of them. It's pretty effective if you do it every night for a week or so.