As much as you need for the final pot
They “should” have greened up with the nitrogen load you gave though I suspect the high dose of Megacrop didn’t help…the soil is probably just that bad. This last foliar is the last “trick” up my sleeve
It is great to have on hand with many uses. I have been avoiding recommending a topdress with it while figuring out the underlying issue…less is more.
They responded well because now they want more sulfur and magnesium after that heavy nitrogen load though getting overfed the other stuff so still reacting…this is why I start with foliars before messing with the soil as it helps uncover the underlying issue when none is apparent