Russian Grow

The leaves began to turn yellow on the cheese, I do not know what it is connected with, either because of the lamp, or it is almost ready, because The manufacturer blooms stated 7-8 weeks. I feed all three plants equally, but during the next watering EC drainage in MWK was about 1000, and for cheese 350 total. Is it really necessary to give more fertilizer? The producer writes that the variety is susceptible to fertilizers.