Nutrient deficiency

Well I guess it's either a nitrogen deficiency or a magnesium deficiency. The symptoms are almost the same (yellowing leaves, older growth first (nitrogen and magnesium are mobile -> can be transported to newer growth) Since you are feeding with BioBizz grow and bloom only, I believe the girls need some extra Magnesium. 1-2ml/l of CalMag (any brand) should be fine. This is only my recommendation: You could increase the amount of BioBizz grow (which is nitrogen) by 1ml/l to eliminate the risk that it is a nitrogen deficiency and simultaneously feed the girls with CalMag. If leaves turn dark green, reduce the amount of BioBizz grow. AND you should always consider that: - nutrients could be locked up in the medium (plant has no access to them) - Ph is too high or too low -> reduced or no uptake of certain nutrients Hope this helps Happy growing