acid cleaning

So after a long period of unemployment, and recently getting a job, I’d hoped to save my pool from having been a bog. Got it blue for a while but it was always cloudy and after finally using HTH green to blue (which I shouldn’t have since I have a single Hayward cartridge and not a backwash...

What is this white chalky paste on the top of the pool tiles (which does not react by bubbling with concentrated muriatic acid)? In the past few weeks I've used a few cases of HASA muriatic acid to clean the tiles which bubbled like crazy on the bottom half, presumably calcium carbonate. The...