We have an in ground pool with liner. The concrete is rather stained, algae etc. I did a test area where I used muraitic acid and a wire brush and it looks shiney and new. However I'm concerned about getting the acid on the metal portion that holds the top of the liner. It looks like painted aluminium and I'm guessing the acid would damage it. Is there a good way to protect this part of the pool when I'm cleaning the deck?