buffering acrlic

If the buffer contains a chemical it is probably a good idea to take the fish out, also to wash the tank really well before setting it up again. Fish can be sensitive to chemicals used for cleaning, in handcreams, insect killers etc. Try to keep all chemicals away from the tank.

I take it you are talking about polishing the outside of the tank. If you are talking about the inside, you would absolutely have to take fish and water out.
 
As I just bought a 185g used acrylic tank, I've been looking for buffers to fix the minor scratches. Novus is a brand that makes buffers for the outside of the tank, but there is a product made by Clear-for-Life that can be used on the inside of the tank with fish and water still in.
 
if your buffing the outside and have any openings on the top of the tank covered i dont see why you have to remove the fish while working on the outside of the tank if your careful.
 
I haven't seen one acrylic tank that has been used for salt water or even fresh for a long time that diden't look awful when empty without water but amazingly most of the scratched and frost disappear like magic once filled back up with with water. I realize if I ever get that used criaglist 200 gallon acrylic light weight tank, I'm just going to have to accept this fact.
 
AquariaCentral.com