Well, to base an educated diagnosis, there is much more information needed eg: pH, feeding cycle, what the N-P-H of your nutrients is, what dilution you are using, how often you flush your reservoir, the sterility of the equipment, etc. The foul smell could be attributed to a number of things like mold & mildew, over abundance of salts in the feeding system, or organic hand-feed fertilizer rotting in the feeding system. If you go through and post the troubleshooter we might be able to get a firmer grasp of what's going on here.

JSG.