hi strange colouring on leaves

just wondering if someone can tell me how my babies are looking there is 1 with a strange colouring they are in all mix about 5 weeks old not been giving any nutrients yet under a 400 watt hps i think after bit of research looks like a zinc deficiency if anyone agrees what would be best thing to give the plant this is only our 2nd grow so any help appreciated

 

I highly (pun intended) recommend that use Super Thrive and Maxi-Crop in EVERY DROP of water that you give your plants until one week before harvest. (These are organic low-level nutrients). At five weeks, they should be much larger than than the plants in the photos. Are you growing organic? If yes, fertilizer should be added to the soilmix a few weeks you plant. That way it has time to leach out into the mix. Some liquid fertilizers will still work, but your choices are more limited. Maxi-Crop should fix the zinc problem.

Soil problems can be more complicated than just adding nutrients. Sometimes the soil is "locked-up." Meaning that there are high salt levels or other problems that make it impossible for the plant to absorb what it needs. In this case, the pots must be flushed out with clean water, then the proper balance of nutrients are added.

 

Considering that it's starting on the outer tips of the leafs and working it's way in it could be a mag def but it could also be zinc.
zinc def:
http://www.icmag.com/gallery/data/500/1134Zinc2.jpg

mag def:
http://www.icmag.com/gallery/data/500/1134Magnesium-1.jpg