I have tried what I can think of, and suggestions thrown at me to clean this algae off of my acrylic tank. (And despite current looks, yes it was algae. I've scrubbed all the color off at this point.)

I've tried scrubbing with wet paper towels (using my nails, the handle of a plastic spoon, and the end of a bamboo skewer to give some stiffness to the paper towel). I've tried scrubbing with vinegar. I've tried scrubbing with H2O2. I've tried leaving vinegar-soaked paper towels on the spots, and then scrubbing. After all of that, it looks like this:

What else can I do?!