OK, I called the manufacturer and he told me that I don't have to etch after grinding. However, I mentioned that I still have some dark spots where the grinder did not grind due to grooves in the cement. He told me that in that case, I should definitely etch and do extra scrubbing over any dark spots in the floor. He also suggested rinsing with a hose and not use a pressure washer.
Well, based on this advice, my brand new pressure washer will stay nice an new for now.
