Plant with yellow tips in younger leaves

Hello, I am new in this forum. I am really lost on what is the issue here with this plant and the problem seems to get worse every day.

I have a small indoor grow room with 3 autos, the three of them have the same soil (comercial soil) and have received same water. Two of them are looking great, but the third started to have yellow coloration in the younger leaves, from the tips growing to the veins of the leaf. Now this has spread to more leaves, not necesarily the younger ones. This seems like a nutrient deficiencia/problem, but then why the other two plants are doing fine? One of the other plants is the same genetics as the sick one. Temp of the room: 25-28° humidity: 65-80% (I know I should lower humidity I am working on that)

Thank you for any advice, its greatly appreciated!!

They all need more magnesium, and less nitrogen. The yellowing is just further along on that one, the rest are soon to follow by the looks. You can use epsom salt, 1 tablespoon per gallon of water. Dissolve well. You can also just give cal mag if you have it, a little calcium would hurt.

To answer your question more directly about the other plants not showing it: Magnesium is a mobile nutrient, so the older leaves will yellow before the newer growth. The soil pH will affect magnesium absorption, but if you're under 7.0 it should be fine.