Yellowing week 5 flowering

correct if wrong -- progressing tip-in and initially started on lower leaves? If so, that's nitrogen. Despite a lot of loud members in teh peanut gallery, a flowering plant needs nearly as much nitrogen as a vegetative plant. So, if you also dropped N significantly like most suggest, that makes it even more obvioous that it is a N-deficiency. Good to use more than one metric to deduce what is goign on... Always ensure pH is not the cause as that can be the root of all problems at any time, though you usually see multiple coinciding symptoms and generally confusing trying to read the plant. Other posibilities -- if starting at top, could be a p-tox. Top leaves will have thinner blades and also may have burnt tips below. If severe, it would also lockout Mg/Ca/Zn/Fe, potentially. K-tox is another with yellow leaves up top.. thin blads and inerveinal chlorosis. That last one is key to know the difference of how the paling progressed... did it start in the spaces between veins or did it start from end (tip) of leaf and work its way in? Like too much P, it locks out similar stuff... and the symptoms related to those things do overlap with what is seen on the plant. Again, the peanute gallery often blindly suggests blasing bloom plants with p/k without any regard to how much an individual is already providing... if soilless or hydro it's easy.. around 6-6.2pH if you are >50-60 ppm P or >200-210ish K, thats entering into ranges that will risk toxicity.. each plant can very a bit, but still the same ballpark. pH will impact these numbers... a different pH can work fine but that will shift what the overall balance should be in your mix a bit. With soil, you can't simply calculate this from your fertilizer, since the soil has it's own charge of nutes too. a little more guesswork invovled. You are in soil, so your pH is likely higher than mine... small differences are likely. so, conisder what you've fed lately, maybe even calculate some ppms used over last couple weeks. eliminate possiblities with info not provided here. With soil, it's such a crapshoot soemtimes.. gotta be familiar with it.. have to know what your soil composition will need supplementation for at various points throughout grow. Anyone that gives a direct answer given this info is smoking a pipe, but so do i, LOL.