We are in week 3 of flowering and the ladies are generally doing well. However the very tips of the leafs are beginning turn yellow, then brown, especially on the new growth. Some of the larger fan leafs are curling at the tips and wilting ever so slightly. Could this be over-fertilization? PH is a steady 5.8, and the temp and humidity seem normal.
It is very possible that it is an over fert problem. It can also be an under fert problem during hydro. The plants need more energy during flowering to produce buds, and if there aren't enough ferts it will begin to draw from itself ie fan leaves. I would flush the system and use a flowering formula.