I actually have a problem with diatoms in one of my tanks too but I use a soft kitchen sponge (since its acrylic) and it works great. I just wiped down my glass tanks last night too and it only took 10mins during a wc. They sell sponge cleaners on a long handle too but as long as its a sponge instead of that scratchy material it shouldn't scratch the paint.
It doesn't look too bad filled up tho, I'm just using mine as a fry tank so it didn't matter much to me lol. The back panel was only halfway painted when I bought it cuz he was still working on it and threw it in with my 240, so I painted the other half with a few coats of some acrylic paint I had laying around and u can't even see where they meet up