It DOES sound like a ph issue to me.....but I don't grow in soil so here's a really good guide to try....pics always help btw.... Good luck.

Revised: The Complete Guide To Sick Plants,pH and Pest Troubles - PlanetGanja.com
Weedhound Reviewed by Weedhound on . Pale yellow leaves, curling downward. Well i cant figure this out, ive gone from seedling to veg growth in the same kind of soil (bayer potting soil, with some lava rock mixed in to promote drainage and aeration.). As of late my plants been getting yellower and yellower whilst remaining a healthy looking green around the venial areas. The leaves also droop down, kinda curling under and into a very loose semi-sphere. Initially i thought it was burn from the lights but ive tested the tempurature all over the growth area and it hovers Rating: 5