Jaunissement, excès ou carence ?

N/P/K/Ca/Mg/S -- Nothing prevents you from having toxicity in one and a deficiency in another. All need to be in a 'happy-zone' relative to stage of life. Also, burnt tips can be caused by numerous things, even a S-deficiency. Looks like a potassium (K) deficiency. Possibly too much N, too - last picture is dark and a bit glossy. N inhibits K, so that could be part of it, but I think it's just exacerbating a shortage and is not the cause of all your visible k-def symptoms. you are in soilless, so this is a bit easier. Check ppms of what you give. I'd expect K to be 180, give or take. N at this stage probably 100ppm and possibly less. In the end the plant dictates. The individual nute ratios can impact each other, so having too much of one thing may require more of another to overcome the antagonistic relationship. But, if the overall formual isn't too esoteric, these numbers should be a good ballpark to make it a bit more of an educated guess than normal. pH somehere near 6 is fine. You go too low and you lockout Ca fairly quickly below 5.5 or so. 6.0 will not be the cause of any problem. My nutes automatically ph-balance to 6.0. 95-99% of plants pull off the same rez just fine and the 1-5% do well enough to not hand-water. Good formula = consitent results. Bad formulas can look great on a few plants and have problems with many others.