I thought I had nute burn on my first grow but it was the HPS too close . I backed it off and was alright till my MH conversion came. I got mine to 2 foot before flowering and it was wasted because not enough side light. I'm right behind you on the size about 6 nodes on the biggset. A little more on the smaller ones and I will start 12/12 at about a foot. The leaves curling down are a prob your missing some thing. I went to overgrow .com and it looks like to much light or too much nitrogen not sure pics would help greatly. then maybe Zandor or some one can say for sure. If you think it's nute you can always flush with ph water. or half your res and fill back up with ph water. The good thing about hydro is when in dought flush with ph water doesn't hurt. When I grew in soil and ounce things started to go wrong it was too late. They could show early signs of sex, 18/6 for a week will show for me. then I can go back to 24/7 or 12/12. Show some pics it will help alot.