I'm having brown spots that will eventually g...

Have a look in the underside of the leaf. They sure to look like mite bites unfortunately. You'll need a microscope though unless you have exceptional eyesight. If you have leaves with those one, I would remove them. Are they more prevalent on the lower leaves. I contaminated my plant with dodgy rain butt water. I spilt some on the leaves, and the water in the butt was contaminated with beasties - learned not to use water butt water from spring onwards (winter is ok as nothing lives in it when it's cold). HTH

It looks more like a calcium deficiency based on you light being too close to the top of the plant. If you raise the light a few inches the problem will go away. You can see that there is a slight mag deficiency as well. But because your light is so close adding additional nutes would not be a good idea just raise the light a little to take the stress off of the plant

Hi there! Stick and Athos have some great suggestions. I've had these types of issues before, and I believe it was related to being out of the proper pH range. If your pH is out of the range, then some nutrients can't get uptaken by the plant -- so even if you have them present in your nutrient solution, the plant might not be getting them and is therefore still having a deficiency. I would definitely make sure you are keeping your pH in spec. I grow in hydro, and pH is supposed to be between 5.5-6.3 generally. I know soil is a higher pH, so don't follow my numbers. Someone can point out the recommended pH for soil (or check GrowWeedEasy.com) -- get yourself balanced and you should see some improvement. I will say, however, that those leaves will not heal -- only new growth will be the indicator as to whether your issue is resolved or not.

Well you are not posting your watering amount so I can't comment on that. BUT I can say for certain that 40 ml/lt is an insane amount of feeding, have you checked the pH and EC/PPM? I would flush the soil and get a pH pen and PPM meter asap

Hi there! Well this can't be overwatering since you don't have any other symptoms, I'm thinking about 'leaf septoria', a disease caused by a fungus in your soil. Are these yellow rounded spots slowly turning to brown? If so, you got a fungus :( Keep us up-to-date and happy growing bro

Take some pictures with your LEDs off and another "normal" light or flash on... I can not see the spots or area you speak of under your LEDs :)