Yellow or Stains?

[rtslh]

Gunite pool. Have a bad case of something. Brownish yellow on 95% of pool. Will not scrub off with wire brush. Shocked pool for a week no change. Tried 2 types of “yellow out” on with sodium bromate other with something else. No effect at all.
Tried to test spots with vit c tablets (apsorbic acid) no change at all.
Keeping Ph low at 7.2. CYA is low. Chlorine at constant shock level. Nothing is working.

 

[rtslh]

Im trying to avoid an acid wash as it peels a layer of plaster away but at my wits end.

 

[rtslh]

Right now i have placed two chlorine tabs on a step and on swim out to see if that will create a change but not holding my breadth.
Also this is a first for me. Usually algae scrubs off.