Could this be an N deficiency? Newb really need help lol

I'm growing purple kush autos and had some questions regarding the colours of these leaves. I've noticed that some of my older leaves towards the bottom of my plant are starting to get spots of yellow lightly. The plants about to be about a month old since I planted it. I've started the nutes (Fox farm liquid line not using solubles) on it about a week ago at 1/2 a teaspoon per gallon. I've only watered once more since the first and I did not do any increases in nutes. I'm running on a 400 watt so I've been using less nutes as I don't wanna kill em. I just wanted to know could a lack of N be the reasoning behind the colouring of these leaves. If so how much more of my Big Grow should I add? And just to be sure should we water with nutes on every watering (My pots usually get light and need watering every 3-4 days)?

Last thing I've also posted some pics of the branches. They seem to be turning purple brownish. Could this just be cause of the strain (purple) or could it also hint towards some nute issues? I'd appreciate all the advice I've also attached a pic of a healthy leaf last...only about 4 leaves near the bottom have yellowing every other leaf looks similar to the last leaf.

is it only on first set of true leaves? if so then it's normal,but otherwise it would be N deficiency

hmm.. hard to say from them pics, tho I see lush dark green leaf`s at the top, and maybe even some clawing ? (clawing leaf`s = to much N in flowering)

so I doubt it, also since its a Auto and a month old, shouldn't use much N now, and the one pics with the tip "burned" (pics 4) could actually show the opposite, but agin Im not 100% here so don't go a do sumthing extreme ..

about the purple of the steams, a lot of strains cary this as a normal trait, so don't worry to much here .. my violator kush do the same ..

I have had the same problems, I added grow Nute, superthrive and the yellowing hasn't been happening. The purple leaf stem is normal I've had it with all my plants almost. If your talking about the regular stem idk about that. Hope I could be helpful good luck.

Thank you guys for your responses. I've been away for a bit and haven't had a chance to give some attention to these plants for the past two days. My bros been watching em. I had em amp up the strength on the nutes to 3/4 teaspoon a gallon to see if that would help. It didn't do the trick as I got to the check them out today and spend some time with em. After examining the leaves a bit more I started noticing brown spots, that require a closer look to see, occurring on the leaves as well and after some research I'm kind of thinking that this might actually be a magnesium deficiency. I read some advice about foilar feeding with some epsom salt. So I got my bro to get some epsom salt and I told em to mix about 1/2 teaspoon of it with a pint of water and spray it on the leaves that are affected; I made sure to get him to do so on the top and bottom.

I've got a few questions now: would you all safely say my diagnosis was correct and this is probably a mag deficiency? Another issue my brother ended up using epsom salt that was scented (he only mixed 1/2 teaspoon in a pint) would this have any detrimental effects to the plant? And would you all recommend I just get off the salt and buy some cal-mag to mix to the watering (or is the scented salt ok?)

could also be cal or mag