This is in Coco and I originally had a faulty PH meter so for the first 3 weeks I was giving them water at a very low PH of around 4.5. Each of my 3 plants all showed different symptoms but I have since corrected the problem and 2 of the 3 are back and thriving except this one. The tips are progressively getting more brown and the curling seems to be getting worse as well. I have been feeding stronger than usual to get them back up to speed after the PH nute lockout I put them through, so maybe overfeed problem? Other two are handling it just fine though so this strain is either super sensitive or its a different problem. I gave them a few feedings at 1100 ppm , then 900 ppm now at around 700-800 ppm. Thoughts?
Looks like a nute burn. I'd stop feeding it anything other than pHd water for a while. Flush them and don't feed nutes until it starts to show new normal growth for a while. Less is always best. Each strain is different in requirements than other strains. Even from seed to seed from the same mother plant can have different requirements.