http://www.sisweb.com/micromesh/acrylic_plastic_hand_kits.htm
Found this doing a search. Apparenlty alot of people use this to buff out scratches on their acrylic tanks. Take some elbow grease though. Good luck!
Nope..thats the top of the skimmer for a Saltwater tank. I dunno about something to buff out the inside. I wouldn't think if you cleaned it out well it would hurt anything.
Hmm..there are buffers you can get for acrylic..i dunno at what point they become inert though. I would try and ask maybe in DIY to see if someone knows of a buffer than can help with the scratches. Its probably b/c the tank was setup and saltwater and while FW people hate algae in most forms...
You could do alot with 100gal! I would make sure its 100 gal first though and have the guy give the measurements of the tank. It seems quite a bit smaller (my 55 looks bigger than that tank) but sometimes pictures are misleading! Good luck!
+1 was thinking the same thing myself. Wonder if more toxic stuff got stirred up with the powerhead. I would leave it off and do water changes as often as needed. Maybe try to get a diffuser and see if you can get more O2 into the water would be my only suggestion. Sorry :(