caused by unnecessary flushing.Guess you flushed it when switching to flower.other weeks photos were all good,nice green plant,didn't need to be flushed.too much water,it absorbed what is in the soil and started to drink from its leaves,showing deficiencies like calcium and nitrogen.keep feeding for 2 weeks,do not feed-water-feed,just feed-feed-feed for a while,using same schedule.That's why I don't do midgrow flush.Totally unnecessary unless you think they are overfed.