Can't seem to fix this leaf issue

This has been getting slowly worse for the last 3 weeks. Can't seem to figure it out, it started out as little spots and I thought calcium deficiency so added calcium nitrate, switched to calcium acetate in flower with no effect. Also added magnesium sulphate in case it was mag def. It slowly turned from little round spots into rusty blotches. No clue what's going on. pH is steady between 5.8 and 6.3, I take it up and down in that range and it makes no difference.
Tried changing the nutrient solution twice and it makes no difference.
This problem seems to be affecting maybe 30% of the plants in the grow, the rest look ok but it seems to be affecting more of them as time goes on.

Strain is gg4 auto
Nutrifield bloom nutes fed at 1.6-1.8ec
Plus Nutrifield bud burst flowering additive, bacillus amyloliquifaciens, bacillus subtilis.
Grown in aeroponics SOG.

I would run straight water for 3-4 days then start nutes back a 1.0 ec with no additives.. Watch new growth for signs of improvement.. See if that helps..

Overfed. Lower strength with more feeds or refills is better than super high ec to try 2 make it all week