If you can fill the tank with water then you can add muriatic acid or vinegar to the water. It is recommended to use a 1/10 ratio so 1 part acid, 10 parts water but seeing as you have a huge tank you could get away with using 4 gallons of acid or maybe even 3 in that ~450 gallon tank. Otherwise, if you can tilt the tank then you can use putty around the coralline areas to seal it off and then soak that area in the solution.
As for buffing, the stuff I use is called Novus scratch remover. If there are visible scratches, you want to use some high numbered sand papers, then use the Novus #3, 2, 1 in that order. I use a cheap buffing wheel for my power drill but you could get an actual buffer.