Are you using anything to keep the res bennies happy like hydroguard or z7 ect... The browning could be the start of pythos. If your res temp is above 21°c then you will be bang on the conditions that dwc killer loves !. Keepn the res below 19°c by any means possible. One great way is to cover all your pots with silver bubblewrap insulation. The kind used for roof insulating or wrapping round Jacuzzi's. It is cheap and works amazingly well. ( check my diary of rdwc for example of the pots duringn heatwaves. worked so well !) You also need plenty of micro air bubbles for the bucket to make surface Dissolvable oxygen . The Ph drop is also a part of the plants deposits back into the res during exchanges. Ideally ,starting at 6.2 and slowly dropping is what you want as it allows the full oh range to help release and uptake the elements from nutes . swing is good and also can be a good indicator of how they are actually feeding too if you check ppm as well. I will put a chart on my current grows BlackBerry week 10 pictures to show you the best way to read a dwc feeding and ph swings meanings and fixes. It is a great way to dial in your feeds to the sweet spot every time. Any lockout issues require a flushing of ph'ed water for a day to reset the root access too. Hope the chart on my BlackBerry fast buds week 10 helps. ( doing it now)