I’ve been reefing for quite a while, and this is the best glass scraper I’ve used so far. It uses safety razor blade you can get 100 for $10. I use Astra brand from Amazon. Blade doesn’t rust and I don’t think there is any oil or anything on it. Since you can use both edges, cost comes down to 5 cents for a new blade edge. I’ve tried really expensive magnet cleaners. Sure they’re convenient, but nothing cleans like manually scraping the glass by hand. I have a small tank so using this may not be practical if you have a large tank.
I 3D printed this
https://www.thingiverse.com/thing:4555029
I 3D printed this
https://www.thingiverse.com/thing:4555029