MightyMagnet :-D
I have an acrylic tank and have had to deal with that plague. I have a plastic scraper (the blue multi angle one that some here will know) and it works well. I also had to hand "rub" it out with filter floss. Both took a lot of effort and time. I got my mighty magnet and it came off with so little effort and time. Tank cleaning is a breeze. It is a combo of the cleaning pad and magnet strength (which is WAY better then the typical magfloat types). Mike got the MM algae sock and used it on his Magnevore (another high end and powerful magnet) and it worked out quite well for him too.
Yes, it is expensive. But if I had know it would make cleaning this easy, I would have gotten one ages ago. It would have saved SO much time.