Generally not one to encounter an issue in life an...

From what I can see, the old lower growth that is yellowing is from those being at the bottom of the plant and no light is getting through your canopy causing your plant to use up its nutrients from those leaves first which is perfectly normal. What isn't normal is I can see some of your newer growth showing signs of mild nutrient burn (yellowing tips) the start of many problems. So i'd actually back off the nutrients a little, maybe for the week and see if she gets better as if you're feeding it nutrients and the nutrient burn gets worse, you'll then get lockout at the roots, which means your plant growth will be stunted and can no longer uptake nutrients. This early into flower you don't want that. Less is more, you can always add extra but you can't take away, so bare that in mind. Your neew growth is healthy, I'd only worry if your NEW growth was coming out yellow etc etc. Pay attention to your temps as well, don't let it go past 30 Degrees C or it will stress your plants Hope this helps

I use Biobizz stuff too, you are using quite a bit of grow and bloom, so it's not nitrogen, actually you feeding strength might be just a little too high, but it's not that either. Have you measured your water's pH and EC/PPM? Something like this happened on my first indoor grow (you can check it om this site too) and found the answer almost at the end of the flowering phase, after loosing most of the fan leaves. I can't see, but do you have purple petioles? It's one of 2 reasons, either wrong pH (I know Biobizz says not to adjust it, but in my case my tap water pH is between 8 and 9 and when I did not adjust it, it gave me plenty of troubles). Or magnesium deficiency, which will make lower leaves dry, curl and drop. In my case it was a combination of both. Get a pH pen and EC/PPM pen too, check your water source (mine was 20 PPM and 8.5 pH), I have to use a calcium and magnesium additive to prevent this from happening, since I developed massive calcium deficiency in the later flowering weeks.