Why dont you plant them , vs pots?

I suspect it may be the water retentive soil mix you use which interferes with nitrogen uptake.

Nearly all citrus prefer a slightly acidic soil pH - 5.5-6.5. Too high a pH reduces the plant's ability to withdraw necessary nutrients from the soil.

You either need to use a potting mix with a lower pH (like for acid loving plants - azaleas, rhodies, camellias) or irrigate with acidified water.

Thanks for the replies . I can't plant them directly into the ground as in the UK its to cold in winter, soil in pots are very free drainage but will look to lower PH. Thank you all.