Hey
Im fairly new mysel but I think it could be either heat stress or a magnesium deficiency.

I'm not 100% but here is a link so you can self diagnose.

Plant Abuse Chart

You can check out my grow here: LED LOGGER

I hope this helps.

Take care
silent leprechaun Reviewed by silent leprechaun on . Diagnosis needed! Yellow new growth This is 3 week old transplants grown in rockwool. RO water source brought up to 650 ppm when this was seen. Temps run from 79 down to 66 degrees in sleep mode (6 hours per day) Not all plants display this problem although all are not growing very quickly. I'm using equal parts sVa and sVb nutes. Humidity is running between 50 and 71 percent And pH is right at 6.8 Any ideas? This seems severe as I see the yellowing in the edges of older leaves as well. Rating: 5