Well none of the pics show nitrogen deficiency. Please explain what you think nitrogen def. looks like so we can correct that. Or you can google it. One sure sign of it is that the lower leaves will yellow as it get stolen from them for the upper leaves. none of you lower leaves show signs of Nitrogen def so you can't have it as it starts there.
There might be both Phosphorus Deff and iron Def. which are both caused by poor pH. Both of those you should have plenty of in there so try to get the pH fixed.
6.1 is WAY too low and will cause problems of all sorts. In soil phos wont be absorbed below 6.2.
7 is the very edge of okay and should be brought back down to 6.5. Iron def happens at 7.0 and higher.
So I bet the third pic is the bubble...
I wouldn't be surprised however if the tin foil on the floor is actually causing the problem I think
MIGHT be phos and is actually sun burn from focused rays.
1) you don't want to use tin foil at all
2) reflection from below is not really good for a plant especially that close.
Tents have a type of reflective surface that disperses the light so it doesn't really come back from underneath and most people have them far away from the bottom anyway. in your small space that tin foil may be way too close...especially since it doesn't reflect light properly.
So I would get rid of the tin foil.
Fill up a 2 gallon watering can and adjust the pH to 6.5. run that much through each plant and let all the run off go down the drain.
You might want to switch to bloom food now that you are in bloom but stay at no more than 1/4 as you do not have a lot of photosynthesis happening.
post some pics a week after the first feeding after they dry out from the flush...it will take at least that long to really see a difference and know.