I think it's a combination of hydroponic and light source, more the light source. I've seen outdoor hydroponic systems using the sun that look just like the soil based plants. I'm really looking into placement of lights for potential problems such as leaf curl and yellowing. Browning of leaves on tomato plants, too.
I'm starting to feel the more powerful light sources need to be further away from the plants. I'm getting leaf curl on bounties growing jalapenos. Plants from the same gardens that are getting leaf curl were moved to an Ultra with a lower power 30w hood before the leaf curl started. The plants on the Ultra are perfect. Same nute content, same distance from the light hood.