You say these plants are only 2 weeks old, but they appear way past the “seedling” stage, so assume that they are actually older then two weeks from clearing dirt. The Cotyledons will provide the plant all it needs for the first few weeks. but your Promix is just peat moss so doesn’t contain any nutrients and from the size of your plants looks like you should be feeding them.was using big bloom just for seedling and i thought i read on here to always add cal mag +
Personally I think a lot of the advice about limiting nutrients for young plants is because many new growers just go ape shit feeding their plants full strength Miracle Grow the minute it sprouts and fry their plants. So “don’t feed your seedlings” is super common (and good) advice because the majority of new growers ARE feeding too early, especially if they’re growing in an amended soil (like Ocean Forrest). But as your cotyledons start to yellow (or your plant has 4-5 nodes) start feed at about half strength and transition up if they appear light green or yellow. (If they’re dark green and/or shinny you’re overdoing it.) It’s kind of like the advice not to overwater - most growers are overwatering, but that doesn’t mean everyone is, and some go overboard (or grow in a medium that needs to be keep constantly moist) and mess up in the opposite direction.
The advice about always using Cal/Mag is often wrong. In your case it might be recommended since you’re using a medium that is 90% peat moss, so unlike typical gardening soil, it’s void of any nutrients. But if you use any of the basic grow nutrients bottles (like Botanicare, Dyna-Gro, General Hydroponics, FF, etc.,) they contain both Ca & Mg. If you’re using tap water you almost assuredly have Ca. (Cal/Mag is two ingredients so just because you might need one doesn’t mean you need both.) And for some weird reason “looks like a cal/Mag issue” is one of the (dumbest) oft repeated “advice” given on every weed forum. In certain growing conditions (like hydro or coco) it is needed. But a ton of new growers misinterpret this to mean any plant discoloration is a sign of a Mg deficiency and throw out this lousy advice (even when people are growing in soil or using common salt based nutrients that contain both Ca & Mg). Better IMO to ditch the bloom and cal/Mag and go with one of the major brands of grow. (KIS.)
Now all that said, I agree with GNick that you might have a light issue as the discoloration looks to be on the top of your plant (on both growing tips and leaves) which is a tell tale sign that it may be your lights. So take his advice in that regard, but also start using a basic grow nutrient (in moderation) to insure you’re plants are getting properly feed.