This showed up randomly yesterday. It's on every leaf of this Northern Lights auto in soil. None of the others have it. Any identification?

Yes, that picture looks different. If it is calcium magnesium deficiency, the pattern looked odd

Seriously appreciate the reply. I think it looks a little different. How about you?

Septoria?

Ph has always been between 6.4 and 6.6... I'm rather anal about that. Using the FF liquid trio (never again) and the soluble trio (also never again), calmag from botanicare each watering and feeding, hi-brix molasses now that it's flowering. That's it.

Questions you have to consider: how much do you water and/or add nutrients and microbes, how about pH level, drainage, pest management, …

Just some thoughts: Knowing nutrient mobility is helpful in diagnosing plant nutrient deficiencies

Once inside plants, nutrients are transported to where they are needed, typically to growing points. Once incorporated by the plant, some elements can be immobile while others can be remobilized. Immobile elements essentially get locked in place and that is where they stay. Those that can be remobilized can leave their original location and move to areas of greater demand. Knowing which are mobile or immobile is helpful in diagnosing deficiency symptoms.

Since immobile elements do not easily move within the plant, when deficiency symptoms occur they show up in new growth. When mobile elements become limiting, they can be scavenged from older growth and moved to where they are most needed, causing deficiency symptoms in older growth.

You look like you have a larger, older growth leaf showing signs of deficiency. This would suggest a mobile nutrient issue. Assuming you don’t have pest and don’t over-, underfeed, don’t over-, underwater, your pH and temp are correct, and you have good drainage, my guess is Mg. Try adding some Epsom salt.

In some cases, the element is in adequate levels, but unavailable due to pH being too high or too low or the soil temperature incorrect for adequate uptake. Other reasons could be too little or too much water or soil compaction/poor drainage.

Macronutrients, Symbol, Mobile in plant, Role in plant

Primary

Nitrogen, N, Yes, Formation of amino acids, vitamins and proteins; cell division

Phosphorous, P, Yes, Energy storage and transfer; cell growth; root and seed formation and growth; winter hardiness; water use

Potassium, K, Yes, Carbohydrate metabolism, breakdown and translocation; water efficiency; fruit formation; winter hardiness; disease resistance

Secondary

Calcium, Ca, No, Cell division and formation; nitrogen metabolism; translocation; fruit set

Magnesium, Mg, Yes, Chlorophyll production; phosphorus mobility; iron utilization; fruit maturation

Sulfur, S, No, Amino acids formation; enzyme and vitamin development; seed production; chlorophyll formation

Micronutrients

Boron, B, No, Pollen grain germination and tube growth; seed and cell wall formation; maturity promotion; sugar translocation

Chlorine, Cl, Yes, Role not well understood

Copper, Cu, No, Metabolic catalyst; functions in photosynthesis and reproduction; increases sugar; intensifies color; improves flavor

Iron, Fe, No, Chlorophyll formation; oxygen carrier; cell division and growth

Manganese, Mn, No, Involved in enzyme systems; aids chlorophyll synthesis; P and Ca availability

Molybdenum, Mo, Yes, Nitrate reductase formation; converts inorganic phosphates to organic

Nickel, Ni, Yes, Nitrogen metabolism and fixation; disease tolerance

Zinc, Zn, No, Hormone and enzyme systems; chlorophyll production; carbohydrate, starch and seed formation

source: Michigan State University.

Just by looking at it, it looks like calcium deficiency. What nutrients have you been feeding the plant and how often? What is the pH and PPM of the soil runoff?

Using calmag? If not get it. Also chill with the feeding. Cut the dosage in half and only do it every 2-3 waterings.