It's only four weeks in. IMO the leaves should be healthy throughout. Think of all the lost photosynthesis from losing those large fans. Too many people accept dying leaves during flower. It's not normal. It's a deficiency.
I have to agree here. The reason for the deficiency is not just natural dying off. The deficiency comes about due to flushing as the plant isn't getting anymore nutrients so the plant is using up the stores that are left in the leaf. That's what causes the actual yellowing of the leaves, not "its time is coming" genetic scenario.
The same thing occurs with clones. For the time, the cutting will be using the energy stored in the leaves until it can form roots and grow new leaves. This use of energy will yellow the leaves.
In the case of the original post, it doesn't matter what the deficiency is.. flush and re-feed with full strength nutes. In a deficiency, you don't really want to try to replace the "missing" nutrients because you may be wrong and who knows just how much to add. The only time you could have such a deficiency is when you're using the wrong nutes. For example, GH Flora Micro vs Micro Hardwater. Same general nutrients but depending on your water profile, you may use one or the other.
If it's a toxicity issue, you'll want to flush to clean the root zone of excess salt and replace with fresh full strength nutrients. The plant will correct itself over time.
So, in any case, flush and follow up with full strength nutes. In my hydro system, I've set up my buckets in such a way that I can empty them quickly, akin to a flush. I replace them with full strength nutes. Currently, I am in the 2nd week of flowering, replaced my nutes for the first tim this morning. I will do this in every feeding which will be about twice a week towards the end in late Feb to early March. This way, I don't have to worry about over/under feeding.
Nutrient issues are less likely to occur in these situations.
