Can be.
There are some strains that will pink up regardless of PH, and an actual Phosphorus deficiency is very rare.
But, generally, if you see red stems and petioles it indicates a low PH lockout.
Easy enough to check, yah?
I used to call it sunburn, because many plants tint their new growth red to reflect excess red and IR until they are old enough to handle it.
So far though, all of mine were PH issues.

Aloha,
Weeze
Weezard Reviewed by Weezard on . new dude grow new to the scene heres week one https://www.youtube.com/watch?v=n2rUxFLt2co here is week two week two and new UFO - YouTube would love any feedback, pointers or tips.... 3x3x5 with 240 watt full spectrum led and 90 watt red ufo auto sweet coffee ryder, northern lites blue auto, and some auto skunk...cant wait for em to get big Rating: 5