First let me say that I only use this on the sides and back glass of my tank (where I'm less concerned about an errant scratch) but far and away the best algae scraper I've come across is this:
- You can get them online for between $10 and $15
- The wide blade reduces the time it takes to clean the glass
- The blades are very inexpensive to replace
- The handle is very stiff allowing you to really get a lot of pressure on the blade (this makes a huge difference)
- The blades are very sharp - easily removes coralline algae in one pass