Sorry, I missed the part about the soil. Why would you use hydropnic nutes in soil? Soil is a buffer, so ph should not be an issue. So it's probably the nutes. Depending on the soil you used, it should have enough nutes in the soil to feed the plants for some time, over feeding will cause nute burn.
feeding hydroponic nutes to a soil medium plant has no real negative effect on the plant, guard. i'd check your ph 6.2-6.8...and if thats not the problem the it sounds like it could be a nitrogen deficency especially if your plants are only 3weeks old.