It's likely that the roots turn brown (rot) from too much moisture, too often, in the cubes....if they aren't stained from nutes....

You still haven't answered my nute mix question.... So what exactly does your nute mix consist of??? And at what rate of each???

DWC is freakin awesome!!! Oh, what size air pump you running for/in them buckets??? I've grown 1/4lb per bucket after 11 days of veg and 49 days of flower....so I can speak from experience on those.... However I have absolutely zero experience with rockwool cubes....so I can't really say 100% what is effecting them...

CGI::::::