There are hobby magnets with a blade attached, or long handled scrapers on the market, just remember to remove the blages and rinse them, the salt water is a real killer.
Tunze make some pretty strong ones but serious $$$... (I know LikesFish had one for sale)
Otherwise Aquamedic make a good one that has the blade attachment. For huge areas of glass the aquamedic scraper has blades about 15cm wide...
ive got a scraper made by aqua h20.consists of a scraper,rake and standard scrubber.the metal scraper works well in removing Calcerious
lol.something i wont sell.ive seen it most LFS.im sure you'll find one in your area.was about R100.00