Need help with yellowing leaves.

[Tb4]

hey everyone, I've got some yellowing of the lower leaves which if I remember rightly is a mag def? I have an outside growing going as an experiment really. Being in the UK we don't get that much sun and when we do it's not very long (joys of living in the uk) I tried growing straight into untreated ground last yr and as I thought they would they didn't last plus the soil had loads of clay which trapped the water really good and was soaking 24/7. This yr I thought I'd go a different route and put the seed soon as it opened into the pot outside, pot size is 37ltr which I filled with 3 bags of £1 multI compost. I just watered with ph water which I carry in everytime, the plant is a afgan skunk auto, it's only just gone into flowering and is already 4-5 foot tall and healthy, I've only just started feeding it 1m bio grow to every ltr of water and 2m of bio bloom to every ltr of water. I open and cover the top of my pot as not to let any rain water change the ph of the soil. Started getting yellowin of the leaves now it's going into flower and understand yellowin of the leaves happen when in flower but too much shouldn't be going on. I'm thinking a bit of calmag would help clear things up? I would be really grateful for peoples thoughts on it many thanks

 

[ryangrovebags]

Looks like a nitrogen deficiency to me, do you have a closer up picture of the yellowing leaves?