Make sure the nutrient levels in your tank are good (<10ppm nitrates and ~0 phosphates). If there is a lot of it growing, you're going to want to manually remove it by hand. Try to keep it from breaking down into pieces and floating around the tank by grabbing chunks. This is easier said than done, but just do your best. Continued aggressive manual removal, low nutrient levels and snails (turbo or cerith) will definitely keep the problem in check. Just be patient, it won't go away overnight. Cheers!