I would be wary of going from soil/soilless into hydro. I have seen that kill several crops for friends. I would try to keep the hydro system sterile, and soilless mediums can often harbor plant pathogens that are kept in check by beneficials, but things can get out of control pretty quick in hydro.

That would lead to root rot, which would lead to physical symptoms like you are seeing there.

If your roots are white and fuzzy then no problem, brown or slimy then you have a problem. imp: