Leaves yellowing from tips and from bottom of plant upwards. Lost as to the cause now.

Foliar application is the fastest way to remedy in the meantime, will need some water-soluble nitrogen, and absorbing through the leaf multiple times a day can help alleviate the deficiency until we get the PH checked, what soil you got?

Alright pal, NPK are the big three, all of them are "mobile nutrients", mobile means the plant can take that nutrient from somewhere else in the plant and take it to make new growth elsewhere. Then there is "immobile nutrients" which presents itself across the plant as a whole at the same time.

Alright pal, NPK are the big three, all of them are "mobile nutrients", mobile means the plant can take that nutrient from somewhere else in the plant and take it to make new growth elsewhere. Then there is "immobile nutrients" which is self-explanatory. It started to yellow bottom first, meaning the plant is drawing from old to give to new, making it a mobile nutrient. Nitrogen but beyond the point... nitrogen can be deficient or the plant is unable to uptake, although we aim for ph of 6.5 because this gives us the best averages across all the nutrients, nitrogen uptakes best at 7.4 but this cuts off several other key nutrients, anywho my point being if you start dipping into the 5.5-5.8 range nitrogen is going to start having a harder time, this is not the best for veg. A couple of things brother, those fabric pots are not as "breathable" as they make you think make sure to have a constant airflow hitting that thing. The day-night swing should stay within 10 degrees if you can help it. 82 is ok, daytime but you should know that temperatures above 77 increase bacterial rate exponentially, why is this important? Moisture left to sit for X amount of time will very quickly turn to root problems that initially appear to be deficiency. 80% of the time it's an environmental control problem preventing nutrient uptake through the rootzones, not a nutrient deficiency. The roots are so tiny right now, but they do not go deep, your soil looks rich and perlite full of air so that's good but it will dry fast, especially at 82, how you water is important, temperature too, I know you scots like cold water, if it's too cold the water likes to sink right to the bottom of those fabrics, the roots receive water briefly and begin uptake but not long after the top part of the medium is dry, and moisture sits deep, if this is left moist, with little air above 77, its game over in flower already unless your ventilation game is on point. Do not raise RH 45-50% is perfect, anything above 50RH% coupled with temps above 77 is prime grounds for bacterial growth, 50-55RH% daytime at 82 ? , If so your moisture content at night would be very very high, the colder it gets the less moisture the air can hold, at night the plant begins the process of cellular respiration it ejects a whole bunch of moisture out of the leaves at night, and you might not notice it now, but as the plant grows it gets bigger, and during flower it increases greatly. So if you have 50-55rh at daytime 82 it may well be spiking above 70RH overnight making it cold and damp with no place to dry, above 70-75rh This essentially forces the plant to close its stomata as a defense mechanism to prevent itself from "drowning" as the little lungs on the back of leaves need "co2" which constitutes 0.04% of the air you breathe, which is why your ventilation game is important. A cannabis plant will droop its leaves very distinctively 16-24 hours before the effect of drought has negative effects on growth, the initial drooping is not "Oh shit IM OUT", "OH shit I'm almost out" Start conserving everything we have left, essentially the same as putting a computer in sleep state, soon as it touches water its back to 100% with a negligible difference. add some inorganic mulch, and rocks to help keep some of the topsoil moisture around a little longer, as the light dries it out it sucks up lower moisture like a sponge, we dont want to dry up so fast where the majority of the roots are, water is the solvent used to transport nutrient, Don't be afraid to let the plant tell you when its time to water, so long as you know you can frequent at least once every 24 hours. Co2 is the most dense at will sit like a foggy dew on the floor if it was visible, like a spooky witches' mist you see on tv, anyway my point being, the co2 you eject while you sleep in your home will gather at the lowest point of the house, if you have a 4" inline suck off the 1-2 inch off the floor you can keep co2 above 1200 with a wife and 2 kids and cat. at night have an extraction fan come on anytime the RH goes above 55-60 at night, keeping it on until the moisture is ejected, moisture left for any amount of time above 77 is what 80% of the pics on this website QUESTIONS category. good luck HAAMISH! AWK AYE THE NOOOO JIMMMMY. Im stoned.

More nitrogen at the least.

Looks to me like they are getting to hot, taco leaves are a tell tail sing, 28c daytime with no fan is a bit much, need to keep the air moving and try and cool it down a bit. ....[][][].... RH at 45% is not ideal but is still within the range of normal in veg I like to see RH aorund 60%. ....[][][].... When growing in coir you should know it is void of nutrients and needs everything provided to it, that's macros and micros NPK CaMgS ZnFe exct.. without it the plant will suffer. ....[][][].... I think your lights height is on point now, its time to fix the feeding and get it watered. With coir and liquid nutrients you want some runoff to avoid any salt build up. PH can be between 6-6.4, there is no reason to have the PH so low around 5.8 as if something happens and the PH drifts then its much closer to danger zone of causing bigger issues. All hydro nutrients can be taken in by the plant in a range of aorund 5.8-6.8 they are readily available and work in a wide range, why limit yourself and titter on the edge of PH lockout. Use a TDS pen to get the EC or PPM of the feeding solution this will let you know how much your giving, can monitor runoff to ensure its not to much or to little. ....[][][].... Good Luck!

Seems hot and dry in your tent...I'd be boosting that humidity to 60-65% with temps that high

Yes these plants are hungry! You are using coco coir, you want to give the plant EC 1.2 and pH 5.7 during this phase of the grow. Move the EC up with EC 0.1 every week till you reached EC 1.8 keep giving EC 1.8 till harvest. Keep the pH stable on pH 5.7 during the entire grow. Also water till 20% from the water that you give is draining from the bottom of the pot!