Purple stem ?

The most common purple problems come from nutrient deficiencies and root zone issues. Phosphorus and magnesium lockout or deficiencies are at the top of the list. Purple stems can also come from nitrogen or potassium deficiencies or lockouts. It can also happen as a result of low nighttime temperatures and also genetics. Other than genetics, another major cause behind discolored stems is strong light exposure. If you use training methods like LST or defoliation, you may notice the exposed stems of your plants turning red, pink, or purple over time. This is completely normal and shouldn’t be cause for concern as long as your lights are sufficiently distanced and your plants look otherwise healthy.