White Widow Auto - Yellow leaves and strange growth with new equipment

Looks like low N. Not too many symptoms overlap. I also second the idea that there is potentially something wrong with your watering habits. Or, it could be exacerbated by the tiny plant / large pot context. From what i understand light mix has a very light charge and then you pretty much treat it like a soilless grow? So, if not watering deep (all the way down) while watring a smaller column due to vast size difference of plant and pot and not getting 10% runoff, that'll eventually have negative effects. It may be fine in the short-term, but risk quickly elevates over time. i think this is just a n-deficiency... but you probably want to amend your proces or watering habits if not adhering to some basic best practices for potted plants, not just marijuana plants. 1) fully saturate - 10% runoff, if soilless is essential. 2) wait for dryback and repeat. I go by loss of weight, others feel depth of dryness... doesn't matter as long as it's consistent and accurate. it should not be complicated. Watering a tiny plant in a big pot requres some adaptation. you water a smaller circle around the plant, not the entire volume, but do make sure that moisture goes all the way down and get some runoff if it is soilless. Otherwise you train superficial roots and get fucked up drying patterns inside the medium which will cause all sorts of root-zone related issues if given enough time. funky build up of nutrients or dry pockets in which roots should be thriving but instead die off etc.. I've done well over 400 up-pots... never once saw a plant slow down or get 'shocked.' Even autoflowers benefit from proper pot sizes and potting up as needed. Your rootball will thank you. Watering is also so much easier with size-appropriate pots. If someone 'shocks' a plant by simply placing it in a larger volume and gently covering it, they should stop gardening altogether -- i say that because i know every single person is capable of doing such a simple task. This is a very low bar of competency to avoid any near-zero risk of problems.

So I looked at your diary. If it is true that your substrate temp is 81 degrees that could be causing the plant to shutdown basically and not up taking nutrients. Its true its is getting deficient but simply more is only going to harm it and not fix the issue. Also if it is true that you ph is 7.8 that is going to cause nutrient lockout due to being incorrect ph for optimal nutrient uptake. What i recommend is rasing your light to the top of the tent or diming it. The air temperature is nearly perfect but you want your soil temperature to be below 72 degrees or it cant supply enough oxygen to its roots which it needs to be able to metabolize. For soil you should adjust you ph of solution anywhere from 6-7 but I aim for 6.5 most of the time. The plants prefer it on the lower end of that range in veg and high up in the range later in flower. your light schedule say 4 hours? i guess that's a typo. . Lack of daylight hours or DLI will cause yellowing too. Could also be light stress too if the leaf temp or light intensity is too high which is a possibility running a new light. Mulch will also help keep your soil temps more optimal.

Yellowing from the bottom could indicate a nitrogen deficiency.

For an accurate assessment, you need some information about the watering behavior.