Weird yellow blotches......

Hey everyone it's me again lol.....

Plant is 3 weeks old, in Sunshine #4 mix, amended with gaia green 4-4-4 and watered with RO water (sometimes with cal/mag supplement). Plants are under a 600w Vivosun LED light set at 24" from top of canopy.

The yellowing is only on the lower growth, anybody know what is causing this?

Looks like a pH issue.
Do you pH your water?

Could also be an issue with your roots as both pH and root issues can look the same.

i do not because the RO water is 6.2-6.3

The pH that goes into your plants is more important then what comes out. Start ph'ing
Your water and both you and your plants will be happy

Yea, I use reverse osmosis water that has a ph of 6.2-6.3

Sorry I had a stoner moment
Every time you said "RO" I was thinking run-off hahaha

Reverse osmosis wateris nearly pure water with a PH of 7. Reverse osmosis is a filtration method that removes more than 99% of all the contaminants in water. The result is nearly purewater, which which has neutral pH of 7. But if it's exposed to air, RO waterdrops down to an acidic pH range of 5

My RO water is 6.2-6.3 stable

Ok well it's a pH or root problem. Wish someone else would join to back me. If you're certain it's not pH, check the roots.

I had major problems when I used RO water, until I started adding calmag to every watering and making sure the PH was in the correct range for the medium( I PH to 6.5 for soil).

Before I had a PH tester, one time the PH of the soil got way off and was causing major problems (nutrient lockouts(deficiencies) and it went on too long (for the THC auto bomb I was growing) and It took too long to get it corrected. So from now on I check the PH of every watering & feeding and I think things are going much better. I’m sure it’s not as easy if you have a bunch of plants.
Good luck