N deficiency in mid flowering? Yellowing lower leaves and tips

Hi all, have read the stickies and whilst I believe this is an N deficiency, I'm not sure how to fix it?

Strain: White Widow Auto
Light: was grow indoor for veg, been outdoor since week 4
Medium: Coco 7 litre pot
Nutes: Canna A and B
Days: Week 6 / Day 47 (flowered around week 4)

Thanks to some good help from this forum I am well into my first grow. I seemed to have no issues at all with it until now. I have been feeding it just Canna A and B at around 1.0 EC from the last couple of weeks. We've had some good sunlight here and the plant put on a lot of mass during its stretch and I am finding myself watering it (A and B to 1EC) more frequently. I am testing PH to 5.8-6.0. Yesterday I tested the run off and it was 5.85PH

On one of the feeds about 2 days ago I added a small (2ml to 4 litres) amount of Canna Boost Accelerator to the feed. Some of the very lower leaves receiving little sunlight had started to yellow at this point but I didn't think too much of it. I don't THINK this was connected to my one use of the Boost and I haven't used it since, but over the last 2 days some of the other lower leaves have yellowed and died and some of the tips of the mid height leaves are yellowing.

The leaves are wet in the pictures because it just started to rain heavy so had to cover them.

Can the plant still take up nitrogen from the roots at this stage, and if so does that mean I should feed at a little higher EC? If not, what can I do to fix this?

Many thanks for your help!

Having looked into it some more - might this actually be a Potassium (K) deficiency, given the yellowing seems to start of the 'teeth' of the leaves?

What temps and RH. are you at. When I see the deep veins and the sides that deep, I relate that to hot or humid.

I see those small spots and they could be water droplets on the leaves it they had gotten water on them when to hot.

All in All they are looking good and you should be fine.

Keep up the Great work and Best of luck to you.

Bear420

As mentioned above, the chattered leaf margins are an indication of a K shortage. Your plant doesn't look short on N in any respect. Good luck.