I have 3 acrylic tanks and cleaning them is a PITA.
IMO lose the mag float - it is sure to get a little tiny invisible piece of sand or rock slough underneath it and viola - scratched tank.
I have used old credit cards and a couple of versions of the plastic scrapers.
The #1 thing you have to use is great care - these things scratch easily and while you can buff the scratches out (apparently) I find it easier to just use caution.
The other option that I seem to going for now is just admiring the coraline growing on the acrylic - you can always have a top down view.
