My girlfriend and I made a grow room out of a closet. This is my first attempt. I am growing 3 amnesia haze auto flowering plants, which are just getting beyond seedling. They have 3-4 nodes. Cotyledons on one started turning a bit yellow. I noticed minimum yellowing on leaves too. We use living soil. I get underground spring fed water locally. (safe to drink and tested) I use pool strips and the ph is low 6's. I use Barrina 2000 LED grow lights. Downloaded phone lux ap and the light is about 40,000 lux. I noticed on the largest plant some darkgreen at leave tips. Is this okay?
I'm not too sure about that, due to being SO young, but it still may be the most logical explanation..
Your 200 watt LED may need a boost, simply get another, at flower, do note led's use U-mol not the trusty lumens or lux 40000lu is about 520-540 u-mols. you need 1000 umols at 12 x12 check Bugbee on YT best method is leave a temp gauge at top most leaf and lower light until you get 77f/25c, I leave a string to dangle as a set indicator ..lol for me that 16 inches good luck
I'd suggest following your manufactures instructions and run your fixture at 50% at a height of 26". I'd also suggest watering outside of your plants leaf tips to encourage outward root growth.
Just wanted to give everyone a follow-up. Plants seem to be doing well. I did buy another light but I don't think I need it yet but maybe for my next grow. I gave it one small dose of sensi cal mag. I started using well water which I think may have more calcium and magnesium. I also heard well. Water may have more silicon which I do not add otherwise. Plants look fairly healthy. I have the lights about 15 in above the top of the canopy. I keep lights between 500 to 650 ppfd.