How far along are your plants in your DWC pots? I experienced this with one of my 1st grows... It was mould on the root system, its a mingin smell, If it is this chances are your roots will be yellow or brown instead of the prefered white.. you can get anti-mould nuits if its in the early stages, or like me ignore it and just deal with a smaller yield, and messy/smelly clean up job after! a good way to avoid getting root rott. is make sure your air-stone-bubbler has not got restricted air flow, make sure your DWC-res. nuits are cooler than grow room temps not icey!! I'd say between 12oC and 18oC and next to no light penetrates the rooting enviroment (keep it real - roots dont see light when in soil
) another good point is to PH balance your tap water in your res to around 6.5 that way the plants will drink up all of what you feed them and not fall prone to illness! remember light.air,warmth,and stale water more often or not will = mould so take super care of being clean and keeping your growroom in check.. Hope this helps - STELTHY