A pool service tech is telling me the stains on my 12 year old pool plaster is scaling and an acid wash using muriatic acid would help! Is there step by step instructions on here somewhere? I just want to double check what he’s telling me is correct! He said put 7 gallons of muriatic acid to my (11,000 gal) pool and a bottle of metal out. Keep the filter running on high 24/7 for 5 days. And brush the plaster at least twice daily. Then balance the chemicals back afterward. Does that sound right?