help i have pale leves and dark veins

hi there. this is my first time growing and i have a problem one of my plants has pale leafs and has dark veins. but i have 4 that are fine. if u can help thanks

Can you list some more information on your grow please.
Age, Lights and distance, PH, Nutrients used, Soil, Watering Schedule ect.
This will really help in the diagnosis.

Im going to assume either a PH or Watering problem. But need to wait for the facts.

am i useing coco soil. feed coco canna a and b 10ml of each in 10 liters ov whater. i give them a paint a day doing ph test no whater when light comes back on.1 600 watt light about 1m away. i have had a heat problem but this stared befor that. age 5 weeks

and a cap ov super thrive in the 10L of water thanks