yellow leaves could be a couple of different things
1) too much water
2) not enough water
to see which ...pull the plant from the pot ...if the soil media feels dry, the yellowing leaves mean not enough water....
if soil media feels wet, then the yellowing leaves mean too much water
yellow leaves might also mean a "change" in the plants surroundings ...like: changes in the amount of watering or amount of sunlight
I have all my adenium elevated for unrestricted drainage
for a healthy plant with a fat stem called the caudex ...use a fertilizer every time you water ....
Your soil mixture could use more rocks and large grain sand to make it drain faster
