Since it is an acrylic tank, you can use a toothbrush and lots of elbow grease. Take an old toothbrush and brush it on wet concrete (or any rough surface) to make the bristles short and uniform in length. Doing so will greatly improve its scowering ability. Credit cards are equally effective but I am not sure if it will scratch acrylic.
To lessen/prevent future occurances of green spot algae, try increasing your PO4 dosages.
To lessen/prevent future occurances of green spot algae, try increasing your PO4 dosages.