Yellowing leaves and strange spots

Thank you so much for answering. I will check the run off PH later today. I know the ph of my tap water is 7.9 so lock out may well be the problem. I was led to believe that Biobizz soil autocorrects the ph levels so I didnt worry about it. I've already been adding calmag for past few weeks at 0.3ml/l levels. If run off ph is between 6-7, should I follow Biobizz reco to up the Calmag to 0.8ml/l to correct possible deficiency? If run off ph is out of range, would you suggest I fully flush the plants and if so do I just use plain ph adjusted water for this? Do I then add back grow / bloom nutrients straight after the flush or wait until next watering once soil has totally dried out?