:shocked: I looked around and the closest thing I could find that looks like that is this. I don't know. I'm sure someone else more qualified will chime in. It sure looks like magnesium def. though.Magnesium is a component of the chlorophyll molecule and serves as a cofactor in most enzymes.
Magnesium deficiency will exhibit a yellowing (which may turn brown) and interveinal chlorosis beginning in the older leaves. The older leaves will be the first to develop interveinal chlorosis. Starting at leaf margin or tip and progressing inward between the veins. Notice how the veins remain somewhat green though as can be seen in figure 15.
Notice how in Figure 16 and 17 the leaves curl upwards like they're praying? They're praying for Mg! The tips may also twist.
This can be quickly resolved by watering with 1 tablespoon Epsom salts/gallon of water. Until you can correct nutrient lockout, try foliar feeding. That way the plants get all the nitrogen and Mg they need. The plants can be foliar feed at Â½ teaspoon/quart of Epsom salts (first powdered and dissolved in some hot water). When mixing up soil, use 2 teaspoon dolomite lime per gallon of soil.
If the starting water is above 200 ppm, that is pretty hard water, that will lock out mg with all of the calcium in the water. Either add a 1/4 teaspoon per gallon of epsom salts or lime (both will effectively reduce the lockout or invest into a reverse osmosis water filter.
Mg can get locked-up by too much Ca, Cl or ammonium nitrogen. Don't overdo Mg or you'll lock up other nutrients.
I would like more info. Soil type, pH, light, nutes, bla, bla, bla... Sorry for the sourness, I just can't help myself tonight. I am serious thought, I need the scoop to lend a hand. I personally am a big fan of making sure my pH is right and then I work on a potential nute def. After I'm sure the pH is stable.
The soil is a seed starter soil. That type of soil doesn't contain many nutrients, a good soil to start with. If the pH is good, then I'd say it is time to feed. Have you fed them yet?
Do you add dolomite lime to your soil? If so, good, if not, when ready to transplant, mix some lime in with the soil, first. It will help stabilize pH within an acceptable range. I believe most people add one tablespoon dolomite lime per gallon of soil. Some add two tablespoons per gallon of soil. I use one tablespoon, and it seems to work well.
Those plants don't look bad to me, good and strong, and new growth isn't showing any problems. They'll grow out of it. As regards how often to feed, that will be different for every grower and dependent on their individual circumstances ie .. soil mix, pot size, age of plant, variety of plant, temperature, humidity etc.
The plant will tell you when it wants more food. Leaves will start to droop when thirsty. You can also go by weight of pot once you've got the feel for it. Growing some Blackberry at the moment, 9 weeks flowering and they get fed every 3/4 days. They'll be coming down real soon
If you're transplanting into promix, I'd say that you shouldn't have to feed for first couple of weeks. That should have plenty in it.