defency travelling up?

That is, no shortage here friend, the yellowing of the low leaves in the pre-flowering is a normal process that makes the plant to redistribute the energies to future flowers, rest assured that it is all right, just remember to always make the plants wet / dry for the soil, if not, the roots do not repirate, take a look also at my plants you will see that they do the same, since they are blooming.

Flush it with like a gallon or so of clean water and use half of what u ised for nutrients every other time u water if its daily or every time if its wvery few days. Could be heat too.