Rust between sugarleaves veins

Could be any of those things said below... I think it looks like light burn. Looking at your diary, the leaves in direct light seem to me the only ones affected. I would raise you light a little and see how she responds. She may have had a growth spurt while you were ill and got a little close to the lights. Good luck and happy growing

Hi There, First of all that problem doesn't seem something too hard to deal with. The previous comments from Hashy and JR1992 are good guidelines. Try that and reply with results. Just also note you're leaves are curling up and have some nute burn too. That can indicate heat stress and too much feeding. Too much feeding most certainly will change the absortion of minerals and the soil PH. Checking and stabilizing all parameters of your grow is a fix for most issues. (Temp, R. Humidity, Airflow, Water PH, EC). Also you should be feeding 2:1 ratio of Bloom:Micro not the other way around. Also I found this article: https://www.growweedeasy.com/overwatered-roots-heat-small-container Hope it helps and good luck.

If your using only ghe micro and bloom then use 1ml micro 2ml bloom. In soil ph should be between 6 and 6.8. Good luck

Might be PH variation yes, check the water drained under your plant, you should check the PH on that water to understand the PH of your soil, and based on that you correct the ph on the water you are probiding your plants