how are magnet scrapers

Mag Floats are good.
 
they're great, but as with all things get a good one - e.g mag-float
 
I bought a cheaper version than the mag-float. So far, I love it!
 
I hardly ever use mine. I just clean off the inside of the tank during water changes and that seems sufficient.
 
I use a mag float. I actually have 2, one is for acrylic (which seems to work well - can't detect any scratches). On the green spot algae, I only use the side of the mag float that goes in the water, and elbow grease (but this is also because the glass surface is curved, so I have to hold it at an angle and use just the edge of the cleaner surface. For softer algae and diatoms, the magnet is powerful enough.
 
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