I understand your questioning and appreciate your attention, however this is a baby grow and I am a currently an unsophisticated grower with little test equipment. No PH tester.

Local outdoor humidity is 15%. I have several cups of water in the grow chamber. Temp is about 85F in the day and 75F at night. Best I can do under the conditions. Airflow is like 60 CFM in a very small area.

I will have to check the soil package later, but it is standard 40% Supersoil potting soil, 40% MG seed starter and 20% Vermiculite.

Again what does it matter if the NPK is off or not if two plants are very healthy and the same genetics while two are struggling?

Water is spring water. Did one feeding of 20-20-20 at 25% of recommended dilution. Will go back to plain water for a while.

No signs of pests or spots or splotching. Leaves appear more bleached than yellow.

For what it is worth, I was an electronic tech for 20 years and am very good at troubleshooting, but this has me puzzled as all the variables appear to be the same for all plants.

If the two smaller ones are female and the two larger ones are male, might they have different nutritional needs? That is the only thing I can come up with.
RackitMan Reviewed by RackitMan on . Leaves Yellowing? It is just about impossible to troubleshoot as I have four plants in identical soil, from the same seeds, same size pots, same watering schedule, same lights and environment, etc. Two are bushy and nice and green and two are much smaller with yellowing, but not sagging or curling, leaves. The smaller ones are propped up to almost the same height as the larger ones. They are 3.5 weeks old and received one weak fert treatment in water. Any thoughts? Rating: 5