Desperately slow growth

What’s the EC of the soil in ms/cm ? It should be written on the bag. Looks like it’s a bit too high for seedlings. I suggest to start seedlings in a light mix for seedlings and clones.

once that clears up, can tackle any nutrient issues.. until then the too intense light could be exacerbating a problem that might not occur otherwise. looks like you need more perlite or similar in that substrate too - improves drainage qualities. maybe, start in a smaller pot and transplant to larger pot when size of plant warrants the increased pot size too. otherwise, it's difficult to irrigate properly. 50/50 for soil / drainage amendment - by volume, respectively. 70/30 for coco+perlite (or similar), because it holds less water per volume. if you water a small circle around plant, make sure that saturation goes all the way to the bottom, or you are promoting superficial roots. if the top is moister than the bottom of substrate, which will happen with bad irrigation habits, the roots turn upward.. they are far less useful when they expose themselves to light, lol... not even roots long after that. just useless stems along surface of substrate. also, a healthy wet-dry cycle occurs when doing it right... reduces risk of pests and pathogens. don't pick a volume to give.. the dynamics of the soil, size of pot determine this. when the plant fits the pot size, you saturate the entire thing -- never leave a dy pocket. overwatering or droopy leaves should not occur while doing this. if it does it is a sign you need better drainage qualiteis in the substrate. frequency of irrigation should not be an issue if sticking to good wet-dry cycle.. wait for top 1" to dry. repeat. keep it simple, stupid (KISS principle)

your nodes looks tightly stacked on top of each other.. .too much light, too early... you stunted it. there should be an internode between nodes... it is part of the anatomy. use its resulting length to help choose light intensity -- can adjust height, dimmer or hours per day to influence this. if you change hours of day, just stay in safe range for bloom or vegetative phases. if autoflower, this matters not. reduce light and within 5-7 days should be exhibiting better behaviour... be ready to increase light later on, as a mature plant can handle more than a seedling can. you just jumped the gun a bit. i find there is quite a bit of variance in what a seedling can handle.. with some plants you may not have this problem while doing the same things... it's fust that seedling was more robust than others and nothing you can predict. so change your process for early stages to be more inclusive. just beacuse 'it worked before' doesn't mean it's best or optimal.

En su diario no tenemos información de ph y ec. Puede que el sustrato esté muy cargado de nutrientes, o pude tener un ph muy alto. Riegue una maseta hasta obtener un poco de drenaje. Con esa muestra obtendrá si los valores del sustrato son óptimos.

Too much water in pot, roots gets no oxygen, plant cant develop. Soil could be too ritch , i see some burns, but those appear on low humidity and hight temps too. If burns were white at beginning - light burn. My advice try to have temps in area of 25-27 cel. Humidity 70. Light not closer than 40 cm, 50 max away. Speay them in the morning with light mist and evening before or straight after lights go off. Lift pot, one looks heavily wet too far from plant. Roots amd leaf has conection. As wide plant is, thats how wide roots went, that circle you have to water, rest not in big pot. Lift them , if very heavy - just spray for 7-10 days, no watering at all. If medium, spray for 5 days, then max 200 ml, better divide in 50 ml and give every 5-10 min, soil saturates better. Mycorrhizae would help a lot for roots to boost up. All the best !

It seems there may be an issue with the temperature inside the tent and the soil. Please ensure that the water you're providing does not exceed 28C, and keep the temperature in the tent below 28C. You can try to cool it down by using water that's around 20C. Cheers! 🍻

The nutrition in soil is a bit strong, and it is too wet. They need a wet to dry cycle. Maybe only water one side leaving the other dry, and switch sides between watering.