Brown spots and yellowing leaves?

I have 4 plants, 3 weeks old, in coco coir. I'm feeding them GH flora series nutrients at half strength, with added calmag also at half streng th. Does it look like this is nutrient burn or a deficiency? And also, does it look like they are healthy otherwise? This is my first grow so I don't have anything to compare them to. Temp is steady at 80F, humidity between 45 and 55, and plenty of air flow. What do yall think?

They look hungry to me. How often are you watering curious?

Every 3 or 4 days, whenever the top of the coir starts to dry out

The bottom leaves always yellow and fall off, plant is using energy for the top. Look a bit overwatered (slight droop), other then that looks good. Count when you water...my solo cups get a 2 count watering, quart a 4 count and so on (depending on plant momentum). Its good to be around 75% dry out by day 3. So just enough water for a couple days