4 1000w HPS? Good lord, man...plan on growing a forest in there? :jointsmile:

Grab yourself a pH test kit, then test the pH of the water you're using. After that, test the pH of some runoff. See where you are from there. If the pH is normal, then you might be looking at a Nitrogen deficiency. Although that is somewhat rare early in vegetative growth...especially when good soil is being used.

Good luck to ya!