Scratches in an acrylic tank. My tank is a 50 gallon 1/2 round acrylic and I have had my share of scratches while installing the live rock column. It is impossible not to end up having some scratches. When the live rock or an SPS touches the sidewall when being installed, or when a piece of sand or snail gets under the magnetic cleaning pad and you end up with scratches in the acrylic.
After a lot of thought, I have developed the following procedure and method to remove them without needing to empty the tank and polish it. It does a good job of taking the scratches out of my acrylic tank and keeping it scratch free. It isn't a fast process, like the old wax on wax off procedure, but you will see them slowly vanish.
I modified my little Magnavore 6 magnetic cleaner by super gluing a 3x4 inch sheet of Micro-Mesh sanding sheet on top of the mesh pad. This allows the sanding sheet to be easily replaced by peeling off the mesh pad. The Micro-Mesh sandpaper comes in ultra ultra fine grits, 1500 to 12,000. This is much finer grit than the normal automotive wet-dry emory paper. I use a 6,000 grit for general cleaning of the inside of the tank every few days.
A newly installed piece of 6,000 will initially show some very slight abrasion on the acrylic if you look very close, but that stops after it is used for 10 or 15 minutes as it breaks in. It doesn't appear like anything is happening when you are doing it, but after 30 or 40 rubs you will see the scratches slowly fad. If you have a deep scratch you can use coarser grits and then go back one the area with a finer and finer grits. You can actually see the fine acrylic dust as you clean and polish. You don't need to use any coarser than 3200 or finer than 8,000, unless the scratches are very deep.
It is a slow manual process but it works very well. You will seen fewer and fewer noticeable scratches, as you use the 6,000 grit in place of the fiber pads, for general tank cleaning. I have never had any of my SPS or Softies coral or fish adversely effected by the fine acrylic dust that develops in the water while doing it. It clears up quickly. Like the fiber pads you need careful not to get a small snail or grain of sand between the paper and the tank surface or it can do more harm than good.
When doing this, I first wipe lightly down the tank outside with Novus 1 or 2 liquid fine scratch remover. Then I cover the outside magnet surface with a piece of paper towel, changing it frequently. It does a great job of polishing both side of the acrylic when doing it in this manner, and it acts as a lubricant to allow the magnet surface to move across the outside of the tank with less effort.
You can buy what is called a Micro Mesh introductory wood kit with one of each of the 3x4 grits samples on Amazon. The sheets aren't cheap, but they work. I buy full size sheets of the 6,000 grit material from
http://www.sisweb.com/micromesh/mmr_sheets.htm and cut it to size to save a few pennies. It is used in woodworking in finishing and polishing varnished furniture.
Hope this helps to take care of a problem we all have with acrylic tanks.
GrahamJr