Here are some pics of my plants. Burn? Not Burn? Deficiency? What is wrong?

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.

What's you ph? And it's be worth checking for spider mites/eggs

pH is around 5.8-6.0. I checked for mites...nothing.

nitrogen def. would be my guess but your ph counds correct. perhaps magnesium, which would mean add some epsom salts.

damn sonny, that shit is over fed with to many nutes...it shouldnt even be getting nutes right now...also either you have the light to close or to far..

I was worried this would happen. One person says deficiency, the other one says toxicity. So the plants should not be getting any nutes at this stage? I"m using R/O water and the light is about 18 inches away. Again, in the past the plants have responded when I flushed them out and just used pure water with no nutes but I figured I have to put nutes in at some point so I just added a tiny but (160ppm) Should I flush them again and just use plain water? If so, for how long?

help help help help

just my two cents but i think you over nuted it. 1200ppm i thought was for semi mature plants, if so that plant looks way to young for full strength nutes..

If i was to gamble, flush and start off with minimal nutes. and maybe check your light setup again..

hmmm....but when I flushed it and then went down to 160ppm which is barely any nutes they started to turn yellow again. So I guess the consesus is that this is not a deficiency.