My dad had been growing for awhile now but he is running into this on a few of his plants. He hasn't changed anything from previous successful grows. Water, soil, nutrients is all the same and fresh.
These were started indoors until about two foot tall and planned outdoor. Zone 5B. Watered daily, no water logging off soil. All three were started from seed and all the are different strain. My dad is very experienced with this but I am not. If I left anything important out please let me know and I'll get the info from him.
I second this opinion. It looks like the early stages of nutrient burn. It could be as simple as not mixing the nutrient solution enough so the bottom of the barrel is hotter than the top. My first suggestion to every grower is always less is more. I like to use super soil up until flower for that reason specifically, and then just use supplemental nutrients twice weekly until flush. Unless you are growing commercial crops on giant plants or are in a CO2 supplemented environment then it is unlikely the plants are getting large enough to require large amounts of supplementation.
He does supplement his tent grow with C02. I will mention this to him and see if cutting back nutrients helps.
It definitely won't hurt the plants. Cannabis is exceedingly resilient, so 2-3 straight waterings to flush should clear out any excess salts if you're using NPK nutrients. If you want some killer mixed medium nutrients I can't recommend Remo's nutrient line enough. It is super easy to use, you can just get away with using the basic line no problem for home grows, and it is EXTREMELY consistent. Worth every penny in my opinion.
One other thought I had. If you are using city water then make sure you are leaving the water out for 24 hours minimum before mixing nutrients or watering the plants. The additives to city water can cause all kinds of weird issues, especially chloramine. The concentration of chlorine/chloramine can vary at different times so it is best to just let the water sit for an extended period if you don't have access to well water or an RO system.
https://www.remonutrients.com/
I think he is going to try the flush and see how that does. My folks have the great well water. He used to test the pH prior to every water but it was always at an ideal level.
Everyone here was so happy to help out with this. This community is great. Thank you everyone.