Unhappy lemon

Hello Everyone

From the photos is anyone able to advise what I am doing wrong please? The tree has many lemons and has flowered about three times this year but I think im doing something wrong judging by the leaves.  the older leaves seem OK, it's the new growth that is washed out. 

I water when it's dry, rain water only, feed chempak citrus food and have started also using baby bio citrus food for the leaves, buts I cannot see any improvement and  worried about running the tree unnecessarily.  

Thanks in advance, any help would be gratefully recieved.