New to forum and new to pool ownership

I have an IG , 18,500 gallon kidney shaped pool. It has 1 drain ,1 skimmer, 3 return jets and vinyl liner . Also Intelliclor salt cell, sand filter , Pentair multiport. I received my Taylor K 2006 in the mail today so I will test tomorrow and post results . I'm having a problem with mustard algae . I think it is mustard based on post in the forum ie looks like sand but is cloud like when brushed . I can't get it off the wall in the deep end (6ft) and when I vacuum from the shallow end it is back the next day . I need professional advice on how to get rid of it. Thank you , I hope I did this properly