razor blade

I don't remember when the Easy Blade came to market, but it's a piece of plastic that you glue to a Magfloat magnet.  Affix a nice clean new razor blade (it's a specific one for this device), and you can work your way around the tank, carving off stubborn algae, coralline, and get into those corners that normal magnets can't quite reach. I like to use it near the sandbed too, so that area is crystal clear to see invertebrates doing their thing. And around the top rim, carving off whatever clings there.  It also takes off calcification on rimless tanks.