Leaves appear yellow under LED

Under LED grow lights (white not blurple) leaves on some plants look yellow-ish between the veins especially the newer growth. Under warm-spectrum room lighting they look fine colorwise.

Still I’m suspecting a possible magnesium deficiency because of some purple stems and some lower leaves have a few dried spots / tips.

Might yellowing show first under LED?

I was hoping that an extra shot of cal-mag next feed and possibly pH-ing the runoff would be enough care. I don’t want to overreact at this stage. Am I under-reacting? Time for flush?

White Widow autos
Coco and perlite
General Hydroponics Flora trio w/ Cal-Mag
About half way through week six and in flower.

Can you post some pic’s

@Deepsix Yes. Pics would help. Had to charge first.

Very purple stem. Other plants not dark like that.

Plant look yellow under LED and has been droopy late in the day. Pot is feeling light but still lightly moist

How much Cal-Mag are you giving her. Could try unscented Epson salt for the Magnesium.


Grow lights change what the plants actually look like (especially blurples). That’s why people ask to post pics in natural light. The droop late in the day is them telling you they’re done working for the day. Under LED’s, Epsom salt (unscented) is a good idea as they tend to make plants more hungry for magnesium. I use 1tbsp per gallon once a week during flower.


Currently giving 2.5ml Cal-Mag / gallon. I just happen to have plain Epsom salt so I will try that.

I’ve just noticed the the runoff from the pot is pH-ing in low sevens. I’ll look into that too.

Thanks all!

I give my girls 5ml per gallon

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