Few of the older leaves have started going yellow with brown spots and shriveling up. I'm in week 7, week 3 of flower. I've been alternating nutes with Plain ph'd water, so only been adding nutes every 2nd water. Have now changed to every water. Is this just due to flowering? Ta
Looks partly like a nitrogen deficiency to me. It also being the oldest growth/not receiving much light also plays a factor. Its to be expected, as long as new growth is green and healthy, nothing to worry about. Hope that helps.
I would have stopped Bio-grow 1 or 2 weeks ago. I also use Biobizz nutrients and I follow this table : https://www.alchimiaweb.com/images/xl/bio-bizz-algamic---5-l_248_4_.jpg
Bio-grow is not required at this stage of flowering for an auto.
The stretch in the first three weeks of flowering uses a lot of grow nutes, what you see is a slight nitrogen deficiency. I use biobizz too, I feed every watering, in my case once a week.
It’s hard for me to tell based on the pictures but it looks like the leaves that are yellowing are the one that don’t receive any light so this would be normal. In fact the plant looks great and you’ve got a nice diary going. Keep it up