Thanks for the replies. The plants are grown in Rockwool cubes and top fed with a nutrient solution every other day (EC 1.8-2.3, pH 5.8-6.5). They are under a 315W ceramic metal halide that provides plenty of light (not too much, not too little). As I mentioned previously, these are just random leaves on otherwise healthy looking plants. This particular one came from a Moruga Scorpion that started as a cutting from last summer's garden. Two other plants have similar issues - Big Jim (from cutting) and Tabasco (from seed) - these seem to be the worst with me picking a leaf or two off every other day. It is not catastrophic at this point; I just want to make it doesn't become that way.