Bottom leaves getting yellow and die

This is definitely a deficiency and not toxicity. Toxicity would have the whole plant very dark green and that is not at all what we are looking at. Nitrogen is a mobile nutrient, so if the plant isn't getting enough from the soil it moves it from the older leaves to the more important new growth. Don't pluck any of the yellowing leaves before you have solved the problem, otherwise you are removing the little nitrogen the plant is able to access. Once the leaves yellow completely they wont go green again, but you will see the yellow wave stop moving up your plant and it will green up nicely again with more N.

at my sight look more like nitogen toxicity/lockout as the plant is few month old and show tips burns even on the green leaf, you should water with distilled water and check the runoff parameter. salt build can block the uptake of nitrogen in the soil by your plant so he moved his reserve to his top. look at Bruce Bugbee nutrients uptake video on youtube..

Could be not enough nitrogen if yellowing is moving up plant. Or she has gotten too dry.

nutrient deficiency, looks like you need to feed that plant