need help diagnosing deficiency asap

Hi I have got some sort of difficancy and I need help with a diagnosis if that is possible, I am growing growing blueberry in coco and I'm 5 weeks into flower

I feeding canna A & B, canna boost and just started using PK 13/14 yesterday. pH 5.8

About two maby three weeks ago
I started to see rust patches in the centre of what looked like perfectly healthy leaves and it has steadily got worse, i now cave two plants that are looking really rough and the others are now starting to show little rust patches and im getting worried.

i was thinking it might be a magnesium or phosphorusAttachment 295993 Attachment 295994 Attachment 295995 problem but im not sure, any advice would be greatly apprecated.