Brown spot help.

An, you are so close to amazing harvest, that if they will lack some shit here and there - it won't change anything a lot. Maintain good watering regime and pH. Ussually people even raise pH a bit, for plant to have harder times to get some elements and force to eat storage. Keep an eye, they will start to drink less, don't overwater, bud rot .... I can agree that it's calcium spots, but from too intense light, from small lack, from pH imbalances or just starting to eat themself - hard to guess always ... Still think , don't care, just push to the End. It should be nice result ! All the Best !

I don't see brown spots either. I did notice the top fan leaves are starting to curl upwards on its serrated edge. That makes he think some heat or light stress is happening. Don't know if your logs temps are correct 28c all around the clock day and night? Might want to try and lower that and see how hot it is on the canopy of the plants is the lights are close. I can't find the composition for your feed on the manufactures web page. It could be lacking in calcium or magnesium that's giving that discoloration but i doubt it. If it lists whats in it. Check for Ca and Mg. or its standardized NPK ratio. https://www.natureslivingsoil.com/autoflower-concentrate They don't really show anything that's in it, just market it as amazing.. Best Of Luck and Happy Growing.

@DrNickerbaucker hi mate I don't see any brown spots however the lighter colored marks on the leaves suggest a lack of calcium and magnesium you may need to add a little epsom salts to your living soil molasses is good too 👍