Week 10 (4 of flowering) Leaves turned yellow. Help please! Newbie.

Hey this is my first grow, and over the past week or so my plants have been turning yellow and starting to curl downward.

Im in week 10 of 12/12 from seed.
Growing THC Bomb.
Using Canna Coco, with Canna Coco A + B neuts,
along with canna Boost, and canna PK 13/14.
Plants are in 6 litre pots.
Using pH of 5.8 or as close to as possible as my pH meter seems to be not working very well currently, and flat out failed to recalibrate today when trying to read a ph of less than 4.8 so ive ordered a new one.
They get watered till run off every 2nd day. And every 3rd watering is plain water.

The plants havent been as well tended as they should over the past 2 weeks as ive sadly been very busy.

They had a bit of heat stress (i think! :/) as they grew right up to my cooltube but ive moved up my light up and that should hopefully be that problem solved.

However they have been turning pale green then yellow and it seems to be starting from the tips and moving inwards.

I think it might be a N problem or Mg.



Should i give them more neuts? and if so what neuts and how much to give?

Or just start flushing?

All advice welcome!

In flowering it would ca-mag with leaves yellowing at top...rw

def cal, mag. maybe even n, which is common during flower

Thanks very much!

Ive actually got some cal-mag but i didnt want to add it until i was sure cause it looks like what a lot of people say it an N defficency.

I'll add it in and see if there is a difference. How long do you reckon it would take for any signs of improvement?