you can avoid scratches by a mag-float by a) being careful not to come within an inch of the sand bed (use a credit card instead), b)covering the outside magnet (the one with the velvet cover rather than the bristles) with a cloth covering, c) not letting the feather dusters and coralline algae accumulate on the glass (be dilligent) and d) remove the mag-float from the tank after use. no guarantees though.
