She is yellow slightly but only between the veins, so yep, probably mag deficiency in beginning stages. When you water, put in cal mag to about 150 ppm or Epsom will do . Then add your nutes to proper ppm or EC for your feed.
They will use more nutes during flip and stretch stage, you should be fine feeding to maintain 1000 ppm runoff, as @MidwestGuy said. Hit them with the cal mag or Epsom in my other post and they should be green and healthy again.
When I zoom in it does look to be the start of a deficiency. I use my CalMag at full strength and also epson salt at a 3/4 dosage. The led’s really make them gobble it up.