Just scrape it off. You can use a bleach solution- 19 parts WATER to 1 part bleach. Dunk your plants in it for a couple minutes and then wash in clear clean WATER.
If you train it to grow (brush algae) on a log or some rocks- when it gets thick it is SO beautiful!
I don't know if this will harm your shrimp, but 3 weeks of using aquarium fertilizer actually killed the brush and beard alage growing on my plants. I know it sounds crazy; using fertilizer to kill plants, but it works.