Getting it off of acrylic can be a tricky business. I use a Kent scraper when mine appears. Either that, or an acrylic safe algae pad. I've found that with regular cleanings, it doesn't have much of a chance to get established and the magnet will usually do the trick. If not, I break out the Kent scraper...
I use the credit card trick too, but if it gets too thick, a peice of acrylic works great and will fit in the same places as the credit card while being quite stiff. Works wonders for those spots where rock/corals and glass/acrylic are too tight for anything else.
Instead of a credit card, or for the heavier build up of coraline, I use a standard home electrical wall socket cover, its great that its plastic and it even has the two holes in it for a firm grip.........much better than a flimsy credit card.
Hey Zack I have to agree with Craig the best scraper I have ever had was a peice of acrylic, comes off like butter.
On the scratches u can buy a kit from Rainbow Life guard that contains all the sanpapers you will need to get them out. Its about 20 bucks and I have used it many times.
Tip: If you get a peice of acrylic as a scraper, get it cut nicely from your supplier. It will have eight sharp edges for scraping. Like all scrapers they get rounded over time, but there isn't a commercial scraper with eight edges as sharp and stiff as acrylic. Just switch edges until they're gone, then buy another. Very inexpensive and effective.
I think the peice I use is about 3/16"- 1/4" thick.
theres also some gritty gel like stuff that Novus window repair sells. You can get it at the Novus shops or at Blue Sierra or some other hobby stores. Its only a few bucks and comes in a few different gritty flavors.
Just a though... If I go with the acrylic idea then my credit cards will be usable and we all know what that means when you're addicted to reef tanks!