Northern Light Auto RQS - 2nd grow

looks a bit lush so something impacting availability of Ca is a possibility too. Also, make sure pH has not drifted too low, as Ca will be one of the first issues seen. the plant needs Ca at all times. so it won't be a 1-time addition to fertilization.. you'd need it each time. With soil, you could amend a bit more garden lime and maybe that eliminates need for something like calmag in addition to your normal nutes, but if it is necessary now, it'll be necessary until the end of the grow. if in soilless/hydro, this is much easier. I assuming your are somewhere around 1.3-1.6 EC (mix of nutes, not including tap water ppm) and 100ppm or more of that should be Ca. YMMV due to various local variables including your tap water. Good ballpark to start, though.

Verge of leaf burn reminds excess of potash. Calcium and potasium correlate , blocks each other if one is in excess, then you overload other, but it cant be absorbed and you have new problem from corecting old. Check ph, most common. Feed autos less, they dont need so much food, plus soil is always full of goodies. She has still 4 weeks, so you have at least 2 weeks of feeding from looking to diary. You never flush in soil. You just stop feeding at final stages, but amount and regularity stays same.