PICTURES. Is this burn or deficiency?

I cannot figure out what I'm doing wrong. I'm a first time grower and I don't know if this is nute burn or a nute deficiency. The yellowing of the leaves starts from the bottom of the plant and works its way up. Always starts at the tip of the leaf and then progresses. I have very low nutes in there right now (160ppm) This all started 3 weeks ago when I had 1200ppm and I thought it was nute burn. I flushed it and used fresh water for three days and then put very low nutes. There is new growth now but they are turning yellow again. Also, the new growth at the top is always the greenest and healthiest. Am I defiecient or toxic? Please help me. I attached some pics I just took tonight.

that thing looks god awful, sorry lol. welp lets diagnose it, but first we need to know things like;

soil; has it been transplanted? looks rootbound as fuck (even though plants can be "rootbound" and still be healthy as long as you nute them)

light; what are you using? the lack of bottom growth + stretchyness indicates it may need the light brought closer.

nutes; ...honestly, i dont know whether that is burn or def..it looks like it was burned and then went deficient.

my honest opinion? kill it and start over, and dont repeat what you did to your next plants. start fresh, use different soil. with foxfarm, its actually difficult to make the plants deficient - ocean forest / light warrior will keep the plants healthy for a good long while.

Yeah i dont know if youre gonna save that one...

I would try adding a tablespoon of epsom salt to a gallon of water, and use that. Looks a bit like a Mg deficiency.