What's going wrong?

small pot, big plant. it'll be tougher and tougher to feed well going forward. using soilless/hydro type nutes that are 100% plant-ready will mitigate that a decent amount, too, but inevitable to occur when the canopy is that much larger than the pot. A good measurement of how effectively you feed, though. the better the formula is, the more robust it'll be / slower it has problems with nute uptake. as far as what you see -- chlorosis on new growth from inside out progression -- could be too much p or k. could be a little low on S, though that would differentiate itself through symptoms quickly. There;s some trace elements that can cause that too, but those shoulld be present, so ensure pH is in a decent zone - slightly acidic. if you made any adjustments lately that jive with the symptoms, Reset it back to the previous formula. the finer things take weeks to show themselves. don't just consider the last few days of time.