For comparison, here's my "Buoi" pummelo leaves look like, before and after:
A moment before sprayed, April 29 2018:
Today:
Like some of you, I also used that same Low Biuret urea from Amazon, at Millet's recommended concentration: 100gr/G with a teaspoon of stickler-spreader; sprayed once under, and once on top of the leaves...
So, a thank you again to our moderator for sharing a good advice, I think my pummelo (and probably my all other citrus trees) leaves look much greener now...