Excel does a great job of preventing this but it requires doing some manual removal. I would take one of those tiny spray bottles from Target's airplane bottle section and fill it with hydrogen peroxide. Pull the plants out and pluck as much of the algae off. Use a paper towel to wipe as much of it off as possible. Then spray with hydrogen peroxide and let sit for 15-30 seconds. Dip to rinse in old tank water after a water change and then replant into the tank.