Bacteria, yellowing of leaves, and smell

So it appears like one and possibly two of my three plants are suffering from nitrogen deficiency. The leaves on top of my largest plant are turning yellow and curling up and dying. The other plant just has leaves that are yellowing. They are 6.5 weeks into flowering. All three are Hindu Kush grown from clones. I use a dual tray ebb and flow system with a universal reservoir. In the past couple weeks I have been mixing in pure unprocessed sugar to stimulate photosynthesis. However lately I have been getting a layer of bubbles on top of the water in the reservoir, and today when my pumps came on there is a horrible smell (literally smells like I took a dump in the closet). I would assume these bubbles and smell are from bacteria that is forming from the use of sugar. Is there any anti-bacterial compounds that I can use to solve this problem? I have a vented hood running 400w HPS at the moment with tempered glass preventing heat from burning the plants. Temps get to a max of 75 at the moment. The bud is extremely crystally and have a bunch of hairs. I plan on going to radio shack in a day or two to get a scope to check trichromes, but I highly doubt that they are ready. To smell the bud you have to stick your nose really close. However to be honest the bud is some of the great looking stuff I have seen in a while.

so any ideas on what I might be able to do to solve my problems would be much appreciated.