Do you have scratches on the inside or outside? Tenecor sells a scratch remover that I think you can use inside the tank with water and inhabitants in there. If you have scratches on the outside, use Maguires Mirror Glaze Fine Cut Cleaner and use an electric polisher/sander - not an orbital buffer (it doesn't have high enough rotation speed). If you have deep scratches, you need to sand with an electric sander with your sand paper getting finer and finer and eventually about 600 (wet). Then use the Mirror Glaze and electric polisher. The Novus 2 and 3 doesn't do the job - especially by hand. It leaves too much haze. Do the way I said and it will come out looking very nice. We did it on the inside and outside of a used acrylic that sat in my brother's garage and which he used to throw all sorts of rock and junk into. Looks like new now! You might see some very, very fine swirls but with water in the aquarium, it disappears.