Brown spots on healthy leaves

Lack of potash and watering qrong for soil, at least few times you added water/food while pot was still moist. Almost can guarantee that, did it myself not once and look was same ...

Hi thanks for replying, everybody. This is a bit silly because I cannot reply to you individually so in the one chance that you ever come back here someday, I will answer to y'all here. This fine lady is an autoflower and has been vegging for more than 6 weeks now (sprouted September 7th and we are October 22th as I type this) She has been fed General Hydroponics FloraSeries nutrients. At 75% strength since she's a short indica and I already killed 2 of her sisters with too much of that stuff). I am feeding her once every week. Someone suggested that since she's been in Veg mode for so long that I should introduce flowering nutrient. I will try that when it's feeding time. Here are some extra informations that could be useful to anybody who wants to help still; Last friday I gave her a flush after I noticed the brown spots. I did a pH test on the runoff water and I discovered that it was something like 4.5 😱 so I gave her pH balanced water with a higher pH than I would normally give to balance things out and it did work. Now both my soil pH and runoff water seems correct. I also had NPK test kit so I can tell you that my Nitrogen was at a moderate level but I was 'very low' for Phosphorus & Potassium so I would assume that Roberts answer might be good. Given these new informations, if anybody with experience wants to help a bro out, feel free to do so. She's the only one of 3 others that died and I don't want to lose her 😭 Thanks!

When I run longer veg like this I usually have to introduce blooming nutrition about week 4 to 6. The plants tend to want more potassium, and phosphorus. I have had the same issue before, and that was how I resolved it.

Check the soils ec level. Slurry test. Ec probably to high.