First Grow Skywalker

Wow your VPD is crazy high. That means your plant is transpiring at a massive rate. VPD is the measurement of vapor pressure in the leaf, as it relates to the vapor pressure in the air (air humidity) With a 78F temp coupled with 30% humidity, your plants Stomata are wide open and cranking up the water and nutrients at a rate that is too fast and can cause excessive nutrient uptake which can lead to toxicity in your plants, and can deplete nutrients in the soil much faster than necessary. Your relative humidity in your space at this stage of growth and at the room temp of 78F your humidity should be up around 70% NOT 30% Get yourself a humidifier, or dump water on the floor of your space. You can roll up a towel and lay it along the edge of your tent and soak it. You can leave a tray in there with water, like a baking sheet or something. The more water surface exposed to the air the high the evaporation rate. Next feed i would do a 400ppm mix at a 6.2 pH The other thing is the plant in question looks like it's suffering from light stress. Back off your light a bit with a dimmer, or just raise it a foot. There is such a thing as too much light and it can cause your plants to bleach white and yellow.

Cold temps, Wrong or lack of right food Light burn Genetics. Last two impossible, genetics goes gradually, light burn effects stems of leaf not plant itself. That leaves you with most probably for me from look - cold temps. But you need at least 18 cel or less, you are far from that range. That leaves you with food issues. You been offered 3 versions Sulphur - bleaching of leaves, going pale , colour from green change to lime. I had once, heavy, you are not in that boat 99.999% Magnesium - yeah, if progressed heavy, stems of plant will get pinky red, but leaves will be way earlier tiger stripy ... Not that case. Potash - most likely if feed was issue, light paling of leaves, red stems of leaves, can progress to plant. Overwatering and lack of oxygen can play such tricks too, but again then you look at stage of leaves and plant, think its not the case too. From look i would say cold night spell, from info - most prob potash.