Hey there HashGirl and Felonious! Sorry I took so long to stop over.. I had asked about the spots on the plants from in the CBD grow community thread. I was hoping I could help out with the issue. Looks like oldbear got to it for you, have you made any adjustments since then to your nutrient feedings?
Lets look into it a bit farther as well.. Are you watering/feeding from above the plant and having the mixture drop over the leaves, or are you just watering straight into the soil? Water droplets alone during the day when the lights are on can cause burn marks on the leaves, the droplets act as a magnifying glass and that is what can cause the spots on the Durban Poisons that I can see. The other thing that could be possible if you are feeding from above the plants is that the nutrient mix is too strong to be applied directly to the plants leaves, just ensure you are watering from below the canopy. If you would like to foliar feed as well, 1/4-1/3 strength nutes are fine for fine mist spraying.
The leaves at the bottom of the Dutch Treats, were they starting to yellow before turning to the curled up burnt looking leaf? Sometimes if a plant is getting low on nitrogen it will start to suck it up from the lowest leaves which can cause them to turn yellow and then crisp up, this will happen from the bottom up. Also, sometimes plants will eventually shed some of the lower leaves on a plant that aren't getting sufficient light or have already served their purpose. Is this only happening to a couple of the lower leaves??
The other thing that oldbear had mentioned about the magnesium deficiency due to the color of the veins on the leaves, I do notice this on the dutch treats but it's on the new growth, sometimes the newest growth can look different from the rest of the plant. It also doesn't hurt to be adding calmag to your feeding schedule especially if using RO water. What type of water are you using?
Hopefully some of this info will help you out and once you get back to me about the questions I've asked we will see if we can narrow things down
Thanks for inviting me over HG, always glad to help out if I can!