While acrylic aquariums aren’t quite as popular as glass tanks, they are still quite prolific in the hobby. The primary reason why acrylic tanks are not as popular is due to how easily they can be scratched. A single grain of sand trapped in a cleaning magnet can wreak havoc on the inside of the aquarium, scratching up the front viewing window and completely ruining the view. If the scratch is on the outside of the aquarium, that’s an easy fix. A little buffing compound and some elbow grease gets that right out. But what about scratches on the inside? Well, if you’re careful enough, you can fix those too. In order to fix an internal scratch, drain the water down to where it’s well below the scratch. Carefully take a rag with a little buffing compound and swirl it over the area, making sure to not get any into the water. Once the scratch has been buffed out, or at least to the point where it’s not longer an eyesore, take a wet rag and slowly rub the area to remove any chemicals. Continue to do this for several minutes, making sure to use a new rag (or a clean spot on the rag) each time. Also be sure to only attempt this procedure one scratch at a time and use as little buffing compound as possible.
I know this may seem like sketchy advice, and it’s not a method I fully back, but it can be done and I’ve seen it done safely.