I just scratched mine
I used my mag float (yes, it's the acrylic safe one) to clean my glass right after I added substrate. I made one swipe and noticed a semi-deep 2 inch scratch write on the front of my tank. I wanted to go ring the mag float peoples necks when it happened, but I learned not to use a mag float when particles are floating in the water. I just wanted to let everyone know not to do this so they can avoid the horrible feeling of scratching your tank. Thanks.