What is causing this?

Hello, as often there’s an insect that eats when there are missing pieces. To solve the problem without resorting to napalm, I use a DIY insecticide made from garlic decoction and black soap, very effective both as a preventive and a cure. The smell is better than nettle tea! Good luck.

Haha gotta love your name! I think that mosquito is right and that this is indeed caused by broad mites Here is a link from an article with pictures so you can compare and an explanation how to identify and how to get rid of broad mites. https://www.growweedeasy.com/cannabis-plant-problems/broad-mites Goodluck! And a happy and healthy 2023

m0use is probably right about the brown spots and nute issues - but you've also got something eating those leaves... some BT (bacillus thuringiensis) will do the trick here no matter what insect is having dinner and can safely be used on flowering plants without damaging the buds or the taste of the harvest (it's organic). The problem is going to be that you need to spray just before lights out so you're going to HAVE to give them some lights out time.... and the plant is so bushy at this point, getting everything sprayed is going to be a pain in the ass but... Good luck!

Broad mites!!

PPM is 310-330. Water temp in bucket is 20.1C. The reason I think it's a pest and not a defficiency it's because I've grown in the same exact conditions in a different location and didn't have any issues.