What causing this?

Good luck with your growing project! Let's take a look at the leaves and roots to identify the possible culprit in this case. - It seems the plant is unable to uptake the nutrients present in the soil, causing it to absorb nutrients from itself, starting with the lower leaves, which then yellow and die. - The upper fan leaves also show signs of having absorbed an excessive amount of nitrogen in relation to the other nutrients. - The lower roots may be suffocating since they are turning a bit yellow. This might be due to the plant being unable to process the nutrients in the soil, but it could also be due to a lack of physical space in the container for the roots to develop and thrive. When looking at a soil pH nutrient absorption chart, pH levels of 7 or more prevent the plant from uptaking essential nutrients like phosphorus, magnesium, copper, iron, and zinc, causing a nutrient lockout that leads to all these symptoms. Ensuring the pH level is closer to 6.2-6.5, along with repotting the plant into a fabric pot of approximately 4-5 gallons, should make your plant healthy again within a week.

Before you begin diagnosing the problem, what is the soil' s ph? If it's too alkaline the plant can't absorb the nutrients. 6.2 is perfect but 6.0 to 6.5 is the range you want to be in. After the ph is corrected I'd feed it a simple tea comprised of coconut water and earthworm casting, and bat guano. Check the ph of your tea 5.5 to 6.0 is ideal. Acids break down organic matter, allowing micro organisms to easily consume and digest them. Don't over feed, be patient and observe.

Pots are way too small, leading to toxic conditions in the root zone, affecting nutrient uptake.

Quite a few issues and/or a lockout. Flush your plant with yucca extract (sledgehammer or something similar) or 5-10 gallons of water. Next feed be sure to double check the PH. Dont give Nitrogen, just something more with P-K.