I was sanding my 250gal tank down and taking all the old paint off and it was hard to remove all the way down to the metal. There is a thin amount of redish primer on it and I was wondering if I had to take it down to the metal?. alot of the tank I could but geting to the sides of it where it want exposed to the element that much it is hard to come off. Should I through it again with a higher grit or finer that is. I was using a 40 and 80 grit 4 1/2 disk.