Ok, just a curiosity question:
I kind of touched upon this in a thread a few days ago about what my fellow acrylic tank owners were using to clean their tank, inside and out.
I used some acrylic safe pads to clean the inside wall of my acrylic tank of algae -- careful to get no gravel in pad. No visible scratches at all. But, when I drained 25% of the water later in the week, I noticed very fine lines here and there along the virgin acrylic, obviously due to contact from the "safe" sponge. When I fill the water back up, presto, the very fine scratches (if we can call them that) disappear. So why complain or worry? Well, I'm not really. Really!
I'm just curious if this is similar to what others experience/see when they drain the water? I guess these lines are akin to micro swirl marks on a car (except they are horizontal, not swirls) and are part of the acrylic experience? To me, this is different than "scratching" the acrylic... or are these the scratches folks fret over and try to remove with scratch removal kits?
True (ugly visible) scratching I imagine results from bumping decor against the sides, trapping a piece of gravel in a cleaning pad and digging into a panel as you wipe, etc. If deep enough, they will show underwater.