Less moisture would be my guess.

Again, I'm NOT a hydro grower,... but root rot and discolored roots in dirt are typically a sign of to much moisture.



Above you mentioned reading something about tomatoes in hydro wanting more O2 to the roots...... how about letting the roots dry out a bit before spraying them again? The dry cycle would allow the roots to breathe in O2 (and believe it or not Roots DO breathe! ) Just an idea.