Yellow bottom leaves whats wrong?

yea like the tittle says heres a photo

How big is the pot that you have it in? You need to fill the pot with dirt up to about 1 inch from the top, half full doesn't give much root space for your plant.

That stem looks pretty thick, how tall is the plant? Are those the only leaves that are yellowing? Can you post a picture of the plant as a whole?

If your plant is big and your pot is small (especially only half full of soil), then it is probably time for a transplant.

...bottom leaves yellowing is classic nitrogen def.

I would say it's most likely a Nitrogen deficiency or they aren't receiving enough light