advice to remove the black acrylic panels from acrylic aquarium

[visu_y]

Good Morning All. Recently I bought a used 350 gallons acrylic tank. It has 1" think acrylic panels. On the side & back, it has additional black acrylic panels (may be 1/8 inch). I would like to remove the side black acrylic panels so that we can see from the side also. I tried to sanding it out with different grits (dry/wet sandpapers), but don't see any results. Do you guys have any suggestions. Please. Thank you.