I would get it out of that pot. the dense soil is having trouble drying and you are using painted clay with no air holes. the roots are starving for oxygen making your ph low if you are useing nutes. If you are not using nutes then the yellow is the same thing as you would turn purple if you held your breath to long. get peat moss and transplant get rid of as much as that dirt as you safetly can. put some air holes down the sides with a pen in the mean time and stop watering