What do you use for water?
That looks like classic toxic salts buildup. Salts build up in the leaf tissue until it basically fries them from the inside.
I get that often even with RO water from low humidity making the plants drink a lot more water that they take up more nutrient salts with. Minerals in tap water make it even worse. They're all salts.
If you haven't flushed already you should. At least the same volume as the pot to reduce the salts in the pot. Soak it good to the point of runoff and let sit for at least a couple hours to make sure any salts are well dissolved then pour thru the amount of water the pot holds. Do it in the bathtub or basin so the water can drain freely. I couldn't move the last one I flushed so used a shop vac to suck up the water as the catch tray filled up. Goes faster if it can drain freely tho.
It won't fix what's wrong but will slow down the progression. Buds will still be good.
You just want it saturated and can remove any runoff while it sits for a while.
When you use the 3 gals for the flush you want to add it as fast as it will take it and run out.
Brita filters don't remove any of the minerals in your tap water. Do you have a ppm pen to check your water with? You can call your water supplier and get a copy of their water analysis report for free. They'll usually email you one. Should have ppm and list all the minerals in your water. Those minerals will build up in your soil with every watering like the scale does in a kettle or coffee maker.
I use RO water only for my plants and BUNN coffee maker to make sure everything runs smooth and if something goes wrong with the plants I don't have to worry that it might be the water I'm giving them.