You are running all those different strains in the same tote? Is that net pot in the front left spot empty? Exposure of the nute solution to the light will cause algae to grow in your res.
Don't give up on the diesel yet--she may still pull through. They look nice and bushy, however the Burmese Kush looks as if it could be having some pH and/or nute problems. What is your pH? Have you started to feed these? If so, what and how much?
i think what thehempgoddess was getting at is that dwc is almost plant/strain specific as far as nute/ph/ppm/etc regimen...
...some plant strains like it hard, some like it soft. ya dig?
most of the time you want to try to put the same plants/strain in the same res and try not to mix strains. ...i've seen mixed strains work on an ebb/flow system with success. i've seen mixed strains work in a dws same-res system, too...don't get me wrong. it's just not advised.
prime example is my outdoor grow...my chemdawgXsourdiesel plant is a nute-wh0re. she can't get enough. ...my presidential kush plants on the other hand barely need/want anything at all. if i had them in the same res, one or the other strain would eventually fail.