Assessment and help!

Thought I would post an update having spread more fertiliser with a proper roller feeder. 1st picture was taken on 20th april. Then a couple of days later I spread the additional fertiliser properly and then took the 2nd photo tonight. It's getting much better but there is still a big difference in the strength and quality of the weaker grass. Any advice or comments welcome incase I need to do anything else to kick on with it. Cheers