Colin is right on the mark, problem algae (and the photos definitely show problem algae) is caused by an imbalance of light and nutrients. Light involves intensity (which has to be sufficient for the plants in the tank but no more), spectrum (this drives photosynthesis so the plants can grow), and duration. Nutrients involves the natural nutrients occurring from fish being fed, plant additives if any, and water changes.
If you can provide some data on all these factors, we should be able to resolve things.