Adjusted the light a little last week and started noticing one starting this. Should I be worried?
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My first guess would be that they are hungry.
Some purpling is genetic. This doesn’t look like that.
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LED lighting will cause purpling of the stem. No worries
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First off what strain? It looks like petioles have purple and the stem a little less but kind of hard to tell from the photo if it’s genetics or stress related. A good sign of genetics is purple striping on the primary stem… Pretty much every strain that I’ve grown which has turned interesting colors had that aspect
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Well I thought I’ve overfed them after seeing a lil nute burn but 
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Unknown bag seed…labeled sour diesel if I remember correctly but who knows what it could be. Took these from clone outdoors and never seen the purple from them until I got into indoor. Purple stem on the leaves is new as well but that started early.
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Well as you know sour d is a notorious lime green type strain so pretty doubtful it would be genetic related especially this early on. But hey you never know man bag seeds can throw you a curveball. when you said you adjusted the light did you ramp up the intensity?
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Here’s an example of purple/red. This plant grew outdoors.
This pheno of Blue Tara turned out some fantastic smoke.
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10-4 both intensity and raised it to the top of the tent. I don’t have a fancy meter for PPFD and the one I do have would work if I could figure out the app 
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As a guy that uses old and new lights I’ve noticed that the modern white high-powered LEDs can sometimes stress younger plants and random strains out resulting in deficiencies. My old blurple and metal halide rarely caused those kind of issues. When the leaves kind of do the wrinkle slight downward curl it’s usually a reaction to getting blasted. But weird enough other plants don’t seem to mind
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The rest are completely fine. Now the others I do have seem to be out of either a different pheno or strain due to its structure (I just throw random bag seed in a jar and didn’t really expect them to germ). All do have the purple stemmed leaves though.
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Genetics always play a role but environment can be a leading factor. Led’s can have a suntan effect resulting in various color stems. This can vary based on light spectrum. In my experience, the Far Red spectrum causes more of the suntan effect. These were grown under Far Red spec. You can see the vertical branches have a lot less color than the horizontal branches. Cheers !!!
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Genetics: Some strains, particularly Indicas and Indica-dominant hybrids, are genetically predisposed to develop purple or red hues in their stems, especially in late flowering or when exposed to cool temperatures. If your plant is otherwise healthy and growing normally, this is likely the cause.
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Cool Temperatures: Lower night-time temperatures can trigger the production of anthocyanins, pigments that give some cannabis strains their characteristic purple or red coloration. Many growers deliberately expose their plants to cooler nighttime temperatures to enhance these color phenotypes.
Probably nothing to worry about unless you start getting blueish leaves. Light intensity can cause purpling, but it doesnt look like anything abnormal.
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Here in winter they are all purple in the summer I have to leave the air at a slightly lower temperature to reach purple tones. But of course it depends on genetics of course,
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Purple stems can be genetics or deficiency.
Could be phosphorus bad ph or other.
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