Week 5 yellowing, N def or just fading?

Running a soil grow, week 5 of flower, and i'm seeing lower and mid-canopy fan leaves going yellow and dropping. pH is dialed at 6.4 runoff, feeding a full NPK profile with my salt mix, roughly 150 ppm nitrogen at this stage. Nothing alarming on paper, but the yellowing is moving faster than i expected. My question is basically this: at week 5, how do you guys distinguish between actual nitrogen deficiency and the plant just beginning its natural senescence fade? The timing feels early to me for a true fade, but i've also heard that some strains strip hard and fast once they flip into the back half of flower. I could bump my calcium nitrate fraction and push nitrogen another 30-40 ppm, but i don't want to feed into a problem that isn't actually there. Greening a fading plant back up this late seems like it could hurt more than help. Anyone with experience here, what are the signs that actually tell you which one you're dealing with?

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Experienced8m ago

Week 5 is early but not crazy early depending on the strain. The thing people miss though is that N def and natural fade actually look different if you catch it right. True deficiency tends to crawl up from the absolute bottom and the leaves go a sickly lime yellow, sometimes with a little curl. Natural senescence is more of a dull olive to yellow progression and the leaves just look tired, not starved. The part of your post i'd push back on is the 150 ppm N framing. Runoff ppm and what the plant is actually uptaking are two different conversations, and at 6.4 some growers are still seeing minor lockout depending on their soil's buffering situation. I'd check your input ppm vs runoff ppm gap before assuming the numbers tell the whole story. That said, the thing that actually tells me whether to feed or leave it alone is the rate. If it's like two or three leaves dropping every few days and holding mostly stable, i let it ride. If half the canopy is going pale over a week, that's the plant asking for something. What's your target finish week? Because if you're looking at a 9+ week strain and you're only at week 5, greening it back slightly with a lighter cal-nitrate bump probably isn't going to wreck your terp finish the way people panic about.