Stain through Old Liner

Have been fighting what thought was black algae all summer . Have been down the road of super chlorinate for 2 days -black algae treatment and the only thing that works to impact it is scrubbing with shock in a sock on end of pole.Got it to a level I could live with but not perfect. Last week started to see some spots about where the transition from side walls to bottom starts or where it transitions to slope in deep end . Sock treatment lightened but did not take away .I tried di clor in sock and it also lighten or faded but not gone. Liner is 14 years old- extremely wet summer with water table at high level . Did some reading and is it possible to have algae/mold come from backside of liner ? I had problem like this about 6 years ago and fought same problem but when it dried up the problem disappeared . Your thoughts -opinions-treatment appreciated

Any additional questions please ask . PH is 7.2 FC - 4.0 Alk 120 Hardness 120 CYA 35 local pool place measured copper at .5 which was I guess the black algae copper algaecide ?