Are these the lowest of the lowest fan leaves?
If so, then you are doing everything correctly, seriously!
Too much phosphorus causes a zinc defiency, but that's not the case here: zinc defs affect new growth- not old growth.
Your fan leaves are dying because they are no longer needed.
Now-- this doesn't mean that it's o.k. for all the fan leaves to die off. But some will die over the course of an aggressive feeding schedule.
Here's why: Leaves store those important nutrients. If the plant is getting everything it needs from the rootzone, it will shed the old storage units. After all, it takes energy to store. MJ is very resourceful that way.
So those leaves that are dying off? Well, they USED to be important. Several weeks ago, they were the fountainhead of storage. Now the plant is pulling all the goodies out of them and using them elsewhere. Nitrogen & potassium are typically the first elements to go, so it will yellow and weaken. The K reduction will make them more susceptible to burn after subsequent feedings. So what happens when you give it a good feeding? The shit shrivels up and dies. Looks terrible, doesn't it?
The last thing you want to do is change or weaken your regimen over a few fan leaves. If this were the second week of vegetation, however, you would be undoubtedly facing a shit-ton of trouble and worry.
I just recently calmed down a fellow on here worried about the same exact problem. I asked him: how do the buds look? How does the foliage around the buds look?
THAT's where the action is happening now.
